Identification and applications of porcine reproductive and respiratory syndrome virus host susceptibility factor(s) for improved swine breeding and development of a non-simian recombinant cell line for propagation of the virus and a target for a novel class of antiviral compounds

ABSTRACT

Porcine reproductive and respiratory syndrome virus (PRRSV) causes serious economic losses in swine. The present invention determined that CD 151 is a susceptibility factor for PRRSV infection by transfecting a cell line which is not susceptible to PRRSV infection (BHK-21) with CD 151, which rendered the cell line susceptible. Because CD 151 can be accessed in cellular material including blood platelets and germplasm, the present invention provides a non-invasive method of screening different swine for susceptibility to PRRSV, thereby improving breeding plans. In the case of a valuable animal, results from such screening can indicate any offspring&#39;s susceptibility to PPRSV. Additionally, the viral RNA-CD 151 interaction possesses high affinity and can be used as a tool to detect anti-viral compounds which can be further improved by using combinatorial chemistry. Accordingly, anti-viral compounds that can block the viral RNA-CD 151 interaction can be developed. Advantageously, transfection of CD 151 into non-simian cell lines can confer susceptibility to PRRSV and these recombinant cell lines can be used for preparation of biologics that will avoid simian cell lines which could be a source of primate viruses in xenotransplanted organs from pigs. Finally, the present invention describes the basic mechanism by which the virus RNA enters a target cell. This novel class of proteins is termed viral RNA entry proteins and a novel class of compounds named anti-RNA Entry Proteins can be used to block the entry of viral RNA, thereby preventing viral infections.

RELATED APPLICATION

[0001] This application is a continuation-in-part of application Ser. No. 09/772,044 filed Jan. 29, 2001.

SEQUENCE LISTING

[0002] A printed Sequence Listing accompanies this application, and has also been submitted with identical contents in the form of a computer-readable ASCII file on a floppy diskette and a CDROM.

BACKGROUND OF THE INVENTION

[0003] 1. Field of the Invention

[0004] The present invention is directed towards the screening of different pig breeding lines by quantitative reverse-transcriptase polymerase chain reaction (RT-PCR) for CD 151 and/or DNA PCR using porcine CD 151. Selection of swine lines which are genetically low in or do not possess CD 151 produces offspring which are less susceptible or not susceptible at all to infection by porcine reproductive and respiratory syndrome virus (PRRSV). The present invention also concerns non-invasive methods for screening live pigs and swine germplasm for susceptibility to PRRSV. Additionally, the invention describes the development of cell lines for propagating high titer stocks for making killed and modified live virus vaccines in non-simian cell lines. Moreover, the invention describes a novel plasmid, useful in transforming previously non-susceptible cell lines into susceptible ones for producing the titer stocks used in vaccines. The invention also pertains to providing a tool for discovery of a novel class of anti-viral compounds that will block the interaction between CD 151 and PRRSV 3′-UTR RNA. This novel class of compounds has been termed anti-RNA Entry Proteins (anti-REPs).

[0005] 2. Description of the Prior Art

[0006] Porcine reproductive and respiratory syndrome (PRRS) is a RNA virus which emerged in the late 1980's as an important viral disease of swine. PRRS is the most important, economically significant disease of the swine industry in the United States and around the world. The origin and evolution of PRRSV is not known. Thus, it is a novel emerging virus of pigs. This disease, which has previously been referred to as “mystery swine disease”, “swine infertility and respiratory syndrome”, or “blue ear disease,” is causing heavy losses in breeding herds of the United States and Canada. A similar disease has also appeared in much of Europe and the virus has been detected worldwide. The disease is manifested in two forms, one causing severe reproductive failure in pregnant sows, manifested in the form of premature farrowings, increased numbers of stillborn, mummified and weak-born pigs, decreased farrowing rate, and delayed return to estrus and the other producing respiratory distress in pigs evidenced by lesions that appear in the lungs of infected swine.

[0007] The reproductive form of the disease is described by Keffaber, K. K., “Reproductive Failure of Unknown Etiology”, American Association of Swine Practitioners Newsletter, 1:109 (1989). The most prominent clinical symptoms of the reproductive form of the disease are spontaneous late-term abortions, premature births (which can be as high as 20-30% of all births) and the farrowing of mummified fetuses, stillborn or sickly piglets. Such clinical symptoms will typically be observed in a herd from 4-16 weeks, or even longer. Stillborn fetuses in affected litters often are in the early stages of mummification, as evidenced by tan-brown discoloration of the skin and post-mortem autolysis. Dome-shaped malformations of fetal skulls is also sometimes seen. The infection of sows may go unnoticed, or may manifest itself by an impaired general condition lasting up to a few days. For example, the sows may go off feed, and experience body temperatures either above or below normal. In the farrowing phase, the sows may exhibit depression, lethargy, pyrexia and occasional vomiting. In some affected herds, up to 75% of all piglets may be lost. The economic consequences of the disease, accordingly, are devastating.

[0008] The respiratory form of the disease exhibits clinical signs which are most pronounced in piglets of 3-8 weeks in age, but are reported to occur in pigs of all ages in infected herds. The diseased piglets grow slowly, have roughened hair coats, respiratory distress (“thumping”) and increased mortality (up to about 80% pre-weaning mortality). To combat the problems associated with infection by PRRSV, vaccines have been developed in an attempt to confer immunity to the current PRRSV strains. The present vaccines are only marginally effective and are all produced in cell lines of simian origin which possess a risk of continuous introduction of primate viruses in swine populations. Findings in preliminary studies of gross and microscopic lesions of piglets affected with the respiratory form of the disease suggest that microscopic lung lesions are an important clinical feature of this disease.

[0009] PRRSV belongs within the order Nidovirales in the family Arteriviridae. Other members in the family include equine arteritis virus, lactate dehydrogenase elevating virus, and simian hemorrhagic fever virus. Currently, there is no known human arterivirus. The PRRSV genome is a positive sense RNA about 15.1 kb in length. Untranslated regions (UTR's) of 156-220 nucleotides at the 5′ end and 59-117 nucleotides at the 3′ end flank the viral genome. The viral genome has eight overlapping open reading frames encoding functional and structural proteins. PRRSV grows primarily in the macrophages of infected pigs. In cell culture, the virus is known to grow in CL 2621, MA-104, MARC cell lines and in primary cultures of porcine alveolar macrophages. All of these continuous cell lines are of simian origin and pose a risk of introduction of primate viruses into swine populations. Entry of the virus occurs by receptor-mediated endocytosis and the receptor has been characterized as a heparin-like molecule. However, the mechanisms of how viral RNAs enter after endocytosis into the cell cytoplasm are not known.

[0010] Replication of arteriviruses is similar to that of the coronaviruses. Genomic and subgenomic (−) sense mRNAs are formed in the infected cells along with the (+) sense mRNAs. Subgenomic (−) sense mRNAs have been shown to function as the principal templates for mRNA synthesis in coronaviruses. Discontinuous transcription occurs in arteriviruses with the formation of a functionally monocistronic, 3′-coterminal, nested set of mRNAs. The common leader is joined to the coding region by consensus intergenic sequences through the junction sequence UCAACC. In mouse hepatitis virus (MHV), a corona virus, interaction of the leader, intergenic sequence and the body of the RNA involves cis and trans acting elements. The 3′UTR's of MHV, coxsackie-, rhino- and polioviruses were shown to be essential for the transcription of the genome. There is little sequence complementarity between the 3′UTR and upstream regulatory sequences for interaction, therefore it may be mediated through RNA-protein-RNA interactions involving the viral or cellular proteins.

[0011] There are numerous studies on the interactions of viral and cellular proteins with 5′ and 3′ UTR's of viruses. Sindbis virus, brome mosaic virus, QB phage and polioviruses require the interaction of certain host cell proteins with viral UTR's for transcription to proceed. Although numerous proteins have been shown to bind to these regulatory regions, only a few of them have been characterized. La protein, poly (rC) binding protein 2, and polypyrimidine tract binding protein are shown to bind to UTR's of poliovirus. Polypyrimidine tract binding protein and heterogeneous nuclear ribonucleoprotein have been shown to bind to the leader sequence of MHV. These proteins are predicted to play a role in mRNA splicing and transportation. Some cytoskeletal and chaperone proteins, like actin, tubulin, and heat shock proteins, are shown to have RNA binding activity. These proteins might play a structural role in viral RNA synthesis or in orienting and transporting the RNA replication complexes to the site of replication.

[0012] The study of host cell proteins that interact with viral RNAs is still in the infancy stage and there is a lack of important information regarding this interaction, especially with respect to host-susceptibility factors. Even in arteriviruses, such as PRRSV, the host susceptibility factors have not been studied. Thus, the markers for swine breeding for increased host susceptibility to PRRSV are not known. However, it is known that different breeds of pigs do differ in PRRSV susceptibility based on experimental infection followed by sacrificing the animals followed by further examination with histopathology and immunohistochemistry for interstitial pneumonia and presence of PRRSV antigen in the lungs.

[0013] Moreover, only simian cell lines provide the cell culture for current PRRSV vaccines which is a dangerous activity. The use of simian cell lines for these cell cultures might accidentally introduce primate viruses of significance into swine lines intended for xenotransplant purposes. Because swine are being increasingly explored as a source of xenotransplanted organs to meet the shortage of organ transplants for humans, the introduction of primate cell lines to swine populations may ultimately pose a risk to humans having xenotransplanted organs. Thus it would be prudent to avoid the use of simian cell lines in swine vaccine preparations.

[0014] Accordingly, what is needed in the art is a method of screening swine for susceptibility to PRRSV infection. Preferably, this screening test is DNA-based and is able to correlate the sequence variation in critical motifs or domains of the susceptibilty gene with low, medium, or high degrees of susceptibility to PRRS. Still more preferably, this screening should be non-invasive and able to be performed on a number of different animal fluids and cellular material, including swine germplasm and whole blood. Still more preferably, this screening is performed on ear notch biopsies for detecting pigs with lower susceptibility to PRRS. Additionally what is needed is a method of using these screening results in a breeding program designed to lessen the susceptibility of offspring to PRRSV infection. Another need in the art is to identify single nucleotide polymorphisms (SNPs) in DNA which impact and correlate with susceptibility resistance to PRRV infection. What is further needed is an understanding of the interaction between genes impacting on PRRSV susceptibility and regulatory elements and/or other genes (cis- and trans-acting factors) affecting the expression and regulation of the genes which are related to PRRSV susceptibilty. What is still further needed is an understanding of the chromosomal organization and location of the gene. What is further needed is a non-simian cell line for propagating high-titer PRRSV vaccine stock to avoid crossover of primate viruses into the swine population. Such a cell line will be especially adapted for vaccines used with xenotransplanted swine. Finally, what is needed is a class of compounds which can block the entry of viral RNA into cells.

SUMMARY OF THE INVENTION

[0015] The present invention solves the prior art problems mentioned above and provides a distinct advance in the state of the art. In particular, through the present invention, methods are provided which allow non-invasive genetic testing for PRRSV susceptibility, selection of swine for further breeding, the development of high-titer vaccines in non-simian cell lines, the development of compounds which can be used for PRRSV treatment, and the detection and characterization of the interaction between the 3′UTR RNA of the PRRS genome and susceptible cell lines, thereby leading to the development of novel anti-viral compounds called anti-RNA Entry Compounds. Additionally, the present invention defines the genomic sequence and organization of porcine CD 151, demonstrates the RNA-binding activity of porcine CD 151, identifies the isoforms of porcine CD 151 in different tissues, and produces a non-simian cell line with a transfected porcine CD 151 gene. Finally, the present invention demonstrates the activity of the whole porcine molecule and identifies the CD 151 domains that impart RNA-binding activity and confer susceptibility to the non-simian cell line, baby hamster kidney-12 (BHK-21).

[0016] Accordingly, one aspect of the present invention provides a method of screening swine using relatively non-invasive methods. For example, a blood sample could be drawn and the presence of CD 151 in platelets could be detected using quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and/or DNA PCRs. Also, DNA PCRs can be performed on each notch biopsy or tail snip from piglets. The knowledge gained from this type of screen could greatly improve swine breeding plans as swine with low levels or even no detectible CD 151 could be selected for further breeding. One example of a swine breeding program which utilizes advantages of the present invention compares the CD 151 levels of an individual swine to a known standard of CD 151. This known standard is generally found by comparing the CD 151 levels from a large number of samples of cellular material (e.g. fluid or tissue) from swine and represents the average level of CD 151 detected in the samples. As different cellular materials from the same animal may have different levels of CD 151, it is preferable to compare CD 151 levels from a cellular material of known origin (blood, blood platelets, sperm cells, germplasm, semen, ova, etc.) with the known standard for that specific cellular material. Moreover, as the known standard represents an average CD 151 level for swine, an individual swine may be selected for further breeding based on their detected CD 151 level in comparison with the average. Generally, it is preferable to select swine with CD 151 levels which are lower than average as this would tend to produce offspring with increased resistance to PRRSV infection. Other methods of screening swine will include identifying desirable single nucleotide polymorphisms that correlate with reduced susceptibility to PRRSV. In this manner, swine having certain levels of CD 151 which place the swine into a particular desired percentile for CD 151 levels and which retain other desirable breeding characteristics would be selected for this further breeding. Preferably, these swine would rank in the lower 50th percentile for CD 151 levels. More preferably, these swine would rank in the lower 80th percentile for CD 151 levels, still more preferably, these swine would rank in the lower 90th percentile for CD 151 levels, and most preferably, these swine would rank in the lower 95th percentile for CD 151 levels. In other words, for this most preferred grouping, 95% of all swine would have higher CD 151 levels than the individual swine being tested. Of course, CD 151 deficient swine could be further bred to produce a “knockout” line of swine which would be resistant to PRRSV infection.

[0017] In a related aspect of the present invention, cellular material in the form of germplasm such as sperm cells, or extended porcine semen could be screened for the presence of CD 151 prior to distribution to breeding facilities. Again, using the same general procedures described above, the knowledge gained from such a screening would be invaluable to future breeding plans and use of large amounts of germplasm. The ejaculation volume in swine is approximately 500 mL and the semen gets further extended so even if the animal is no longer on the farm or has died, or has been sold, the germplasm from a valuable boar can be used for many years and for many sows and could provide several future generations of piglets of desirable genotype or genetic makeup. Such frozen germplasm can also be screened for CD 151 levels and PRRSV susceptibility before artificial insemination. This screening could also indicate the susceptibility of animals or their offspring to infection by PRRSV as higher levels of CD 151 are correlated with higher virus production and release by cells. Thus, these tests will also be applicable for screening live animals on farms for their susceptibility to PRRSV. The selection of swine for further breeding based on CD 151 levels detected in germplasm would proceed as follows. A sample of germplasm would be taken and the amount or level of CD 151 in that sample would be determined by RT-PCR. This result (the amount of CD 151) would be compared with known standards for that sample as different types of germplasm would typically contain different amounts of CD 151. The known standards would be determined by the average of the quantitation of a large number of such samples. Swine exhibiting reduced levels of CD 151 in comparison to the standards (and thereby having a reduced susceptibility to PRRSV infection) yet still possessing other valuable breeding traits would be selected for further breeding. Preferably, these swine would have CD 151 levels lower than about 50% of all swine tested. More preferably, these levels will be lower than at least about 80%, still more preferably, at least about 90%, and still more preferably, at least about 95% of all swine tested. In other words, the CD 151 levels in the samples from these swine would be ranked approximately in the bottom 20%, 10%, or 5% of all swine tested. Of course, many variations of this breeding plan could result using the methods of the present invention and these variations are presumed covered provided that the level of CD 151 in a sample of cellular material is determined and this level of CD 151 influences the breeding strategy.

[0018] The present invention also provides a method of ascertaining the susceptibility to PRRS infection in animals. Such a method would include the steps of obtaining a sample of cellular material such as tissue or fluid, performing a CD 151 assay on this sample, and using the results of this assay as a measure of the animal's susceptibility to PRRS infection. The cellular material chosen for the assay can be any cellular material including any fluid or tissue or semi-purified or purified cellular preparation which contains detectible levels of CD 151. For example, blood, blood platelets, germplasm, sperm cells, ova, and semen all contain detectible levels of CD 151. One preferred assay would include the steps of extracting the RNA from the sample and then performing RT-PCR on the extracted RNA. Preferably, the results would provide a quantified amount of detected CD 151. This quantified amount (or level) could then be compared to a known standard for CD 151 levels, thereby indicating the susceptibility to PRRS infection for the animal. Still more preferably, the cellular material sample would be derived from a known origin and the known standard would represent the known standard for cellular material of the same origin.

[0019] The present invention further provides a method for determining if an animal is resistant to PRRSV infection based on the presence or absence of CD 151 in cellular material. If CD 151 is absent, the animals will typically be immune to PRRSV infection. If CD 151 is present the animals will typically be susceptible to PRRSV infection to varying degrees based on the actual CD 151 levels. In this manner, PRRSV infection resistance in animals can be classified based on the detected level of CD 151 in any sample of cellular material. Such a method would include the steps of obtaining a sample of cellular material from the tested animal, performing an assay on the sample to find the CD 151 level of that sample, comparing the CD 151 level of the tested animal with a known scale of CD 151 levels wherein the known scale corresponds to a specific degree of PRRSV infection resistance, and finally classifying the tested animal's PRRSV infection based on the comparison with the known scale. Preferably, the sample of cellular material will be of a known origin and the CD 151 scale will represent the scale for cellular material from the same origin in other animals. Such a classification may result in a percentile ranking of PRRSV infection resistance in the animal.

[0020] In another aspect of the present invention, in vitro diagnostic tests for detection of the wild type virus as well as antibodies to the virus are developed. Such tests generally include the steps of obtaining a sample of cellular material from an animal, performing a diagnostic test designed to detect either the antibodies to the virus or the virus itself in a recombinant cell line, and using the results of the testing to confirm the diagnosis of PRRS in an individual swine or in a swine herd. Preferred diagnostic tests include virus isolation assays and immunodiagnostic assays such as ELISA, indirect fluorescent antibody tests, and indirect immunoperoxidase tests. Preferably, the recombinant cell line used will permit greater replication of the virus making the test more sensitive to PRRSV infection or antibody presence.

[0021] In another aspect of the present invention, higher titer PRRSV vaccines could be developed in CD 151 transformed cell lines to aid in the immunization of swine herds. In a related aspect of the present invention, other non-simian cell lines can be transformed with CD 151 and used to propagate high titer PRRSV vaccine stocks. This has become more of an issue as xenotransplantation (especially in swine) becomes more developed. Use of vaccines made in simian cells may transmit the simian viruses to swine, and hence, organs used for xenotransplantation may also be susceptible to some of these primate viruses. Thus, it will be much safer to avoid using the primate or monkey-kidney cell lines for PRRS vaccines and thereby eliminate the risk of subsequent primate virus introduction into the human transplant recipient population. For cell lines which are already susceptible to PRRS infection, transformation resulting in even higher production of CD 151 can be accomplished using methods of the present invention.

[0022] In another aspect of the invention, non-simian cell lines are transfected with non-simian CD 151 in order to produce a transformed cell line. In this respect, it is preferred to transform non-simian cells with non-simian CD 151 in order to completely avoid primate virus introduction into the human transplant recipient population. A particularly preferred non-simian CD 151 sequence is provided as SEQ ID No. 14 which represents the first complete genomic sequence of porcine CD 151. Preferably, sequences having at least 84% sequence homology with this sequence will be used to transform cells for purposes of the present invention. More preferably, the homology to SEQ ID No. 14 will be at least 90% and still more preferably, at least 95%. Most preferably, the homology to SEQ ID No. 14 will be at least 98%.

[0023] Another related aspect of the present invention will be that the high titer vaccines propagated in non-simian cell lines can be used for other applications such as development of diagnostic tests for detection of antibodies against PRRS, such as an ELISA assay.

[0024] Another related aspect of the present invention is the development and use of a plasmid or vector capable of transforming cell lines and enhancing their susceptibility to PRRSV infection. A particularly preferred plasmid in this respect has been given the designation pKSU (Genbank Accession Number AF 275666), and contains the sequence which is provided herein as SEQ ID No. 1 and is also described in FIG. 1. Preferably, sequences having at least about 91% sequence homology or 93% sequence identity with SEQ ID No. 1 are embraced by the present invention, whether the sequence appears as an isolated sequence, in a plasmid, or in another suitable vector. More preferably, such sequences will have at least about 95% sequence homology or 97% sequence identity and still more preferably at least about 98% sequence homology or 99% sequence identity with SEQ ID No. 1. It is believed that this sequence represents the first reported isolated simian CD 151 sequence. Of course, the corresponding amino acid sequences for this and similar sequences are also presumed covered by the present invention as their determination requires no more than routine skill in the art. When it is desired to use non-simian CD 151 in the development of a vector or plasmid for use in transforming cell lines, sequences having at least 84% sequence homology with SEQ ID No. 14 are preferably selected for inclusion in the plasmid or vector. More preferably, the sequence selected will have at least 90% sequence homology and still more preferably at least 95% homology. Most preferably, the homology will be at least 98% in comparison to SEQ ID No. 14.

[0025] Similarly, the present invention provides a method for incorporating CD 151 coding sequences directly in the genome of an animal. This method generally includes the step of integrating the sequence of interest (e.g. CD 151) into the chromosome using a vector designed for such an insertion. In other words, the sequence of interest is incorporated into a retro-viral vector and this retro-viral vector is used to integrate the sequence directly into a chromosome in the genome.

[0026] Accordingly, methods for preparing PRRSV vaccine stock are provided by the present invention. In general, to prepare PRRSV vaccine stock, a cell line is provided and then transformed with CD 151. This cell line can be resistant to PRRSV infection, or can be susceptible to PRRSV infection prior to transformation. The resultant transformed cell line is then infected with PRRSV and caused to produce PRRSV progeny for use in the vaccine stock. As noted above, the cell line is preferably of non-simian origin. In this manner, cell lines which are previously not susceptible to PRRSV infection are rendered susceptible after transformation with CD 151 and cell lines which were previously susceptible to PRRSV infection produce much greater numbers of progeny virus. Preferably, the transforming step includes stable transfection with a plasmid containing a CD 151 DNA sequence. The CD 151 sequence can be derived from any animal which has CD 151. Preferably the CD 151 is porcine or simian CD 151. When the CD 151 DNA is of or desired to be of porcine origin, the sequence should have at least 84% sequence homology with SEQ ID No. 14. More preferably, this sequence homology should be at least 90% and more preferably 95%. Most preferably, when the CD 151 DNA is or desired to be of porcine origin, the CD 151 should have at least 98% sequence homology with SEQ ID No. 14. When the CD 151 DNA is or desired to be of simian origin, the CD 151 DNA sequence will have at least about 91% sequence homology with SEQ ID No. 1. Still more preferably, the CD 151 DNA sequence has at least about 95% and still more preferably at least about 98% sequence homology with SEQ ID No. 1. The resultant vaccine stock is of higher titer than was previously obtainable prior to transformation. In some cases, this vaccine stock's titer is about 100 fold higher than was previously possible.

[0027] In another aspect of the present invention, polymorphisms in CD 151 sequences are detected and identified using RT-PCR followed by sequencing or a specifically designed test. These different polymorphisms are then analyzed to determine their effects on PRRSV susceptibility. The use of SNPs in this regard is very helpful and such methods have gained wide acceptance for determining disease susceptibility and the evaluation and selection of breeding swine. Moreover, the level of CD 151 may be affected by regulatory sequences, such as promoters of the gene. The regulatory sequences are then analyzed to know tissue specific differences and differences among individual piglets. Additionally, the information obtained from the chromosomal localization and localization of the gene can be used to select the lines of pigs for disease resistance. Of course, collateral effects on important production traits should be monitored in order to reach a balance between any positive and negative effects that occur from the selection for disease resistance traits.

[0028] Still another aspect of the present invention is the development and use of anti-RNA Entyr Proteins (anti-REPs) by the Northwestern strategy. Anti-REPs will be an important addition to the arsenal of drugs against emerging viruses. It is now believed that novel emerging viruses will all be RNA and most likely will emerge in wildlife populations due to encroachment of humans to wildlife habitats. These anti-REPs are extremely useful because they provide a readily available strategy that can be used for viral diseases that may emerge in animals (both domesticated and wild) and humans in future. It is important to understand the identification and mechanisms of RNA-binding proteins such as CD 151 for PRRSV and discovery of the compounds belonging to the category of anti-REPs. One potential method for blocking the entry of PRRSV into cells includes the step of blocking PRRSV viral RNA from interaction with CD 151. This blocking is preferably accomplished by contacting the cells with an anti-viral compound, preferably an anti-REP compound. These anti-viral compounds will be designed to occupy binding sites on CD 151, thereby blocking this viral RNA-CD 151 interaction. Preferably, these anti-viral compounds will have a greater affinity as well as a greater avidity for these binding sites than the PRRSV viral-RNA and should be producible in a high throughput manner.

[0029] Another aspect of the present invention is the ability of CD 151 to bind to RNA and this is the first report of a tetraspan molecule having RNA-binding activity. This discovery can be used to develop a novel class of compounds that prevents PRRSV or viral RNA-binding to this tetraspan and thus being released into the cell cytosol from the endosome. Combinatorial chemistry and screening by a high throughput screening system can be used to find lead compounds to treat PRRSV and potent anti-REP compounds can be found by a modified Northwestern assay.

[0030] With respect to porcine CD 151, the present application defines the genomic sequence of porcine CD 151 and determined that porcine CD 151 mRNA has about 84% sequence homology with known CD 151 sequences from monkeys, mice, rats, and humans. However, it was determined that the intron portions of porcine CD 151 shared little to no homology with other known CD 151 intron sequences. The sequence of porcine CD 151 is provided herein as SEQ ID No. 14. Due to the lower homology shared between porcine CD 151 and the other known sequences of CD 151, sequences having greater than 84% sequence homology are considered covered by the present invention as no known CD 151 has such a high degree of homology. Preferably, the sequence used to practice the present invention will have at least 90% or even more preferably at least 95% sequence homology with SEQ ID No. 14. Most preferably, selected sequences will have at least 98% sequence homology with SEQ ID No. 14. Furthermore, when constructing CD 151, it is preferred to use exons and introns which have similar homologies to sequences listed herein as SEQ ID Nos. 15-29. In other words, it is preferred that all portions of the CD 151 sequence share a certain degree of homology with SEQ ID Nos. 15-29. In the case of the exons of CD 151, the homology is preferred to be at least 84% for each of the discrete exons listed as SEQ ID Nos. 15, 17, 19, 20, 22, 24, 26, and 28. More preferably, the homology is preferred to be at least 90% and still more preferably, at least 95%. Most preferably, each CD 151 sequence should contain sequences which have at least 98% sequence homology with each of SEQ ID Nos.15, 17, 19, 20, 22, 24, 26, and 28. In the case of introns, the homology need not be so high as the porcine CD 151 introns shared no homology with any known sequences.

[0031] It was also determined that porcine CD 151 is expressed at high levels in heart, muscle and endothelium. Furthermore, methods are provided which permit for the screening for porcine CD 151 in pigs by a more user-friendly PCR test on ear notch biopsies or semen and ova samples.

[0032] Porcine CD 151 was also shown in a northwestern assay to have RNA binding activity with the 3′-UTR of PRRSV and that this activity is localized in the exodomains of CD 151 exodomain 1 and exodomain 2 by North-Western mobility shift assays. Finally, the present invention demonstrates that the amount and isoform of porcine CD 151 varies between different porcine tissues depending upon the type of tissue, the age of the pig, and the breed of the pig.

[0033] PRRSV is a positive sense RNA virus causing serious economic losses in swine. Previous studies have shown that 3′UTR RNA of the arteriviruses plays an important role in the replication of the virus through the interaction with the cellular proteins. A cDNA library of MARC cells was constructed in the λ ZAP Express vector and the library was screened with positive sense 3′UTR ([α-³²P] UTP) RNA of PRRSV. A RNA binding clone with an insert of 1.4 kb was found, and, after sequencing, it exhibited homology to CD 151, a transmembrane protein belonging to the tetraspan family of proteins. The MARC and BHK-21 cells were transfected with the CD 151 plasmid, and the fusion protein was immunoprecipitated with anti-Lac Z and anti-CD 151 antibodies. On Northwestern blotting, the precipitated 29 kD protein interacted with the radiolabelled 3′UTR. The precise function of CD 151 is not known, but it has been shown to play roles in cell-cell adhesion, regulation of vascular permeability, and transmembrane signaling. The BHK-21 cell line lacks CD 151 and is not susceptible to PRRSV infection, but when the BHK-21 cell line was transfected with the CD 151 plasmid, it became susceptible to PRRSV infection. Similarly, the non-simian cell lines can be transformed with CD 151 and used for PRRSV propigation to high titer.

[0034] In order to identify cellular proteins that bind to 3′UTR of PRRS virus, RNA ligand screening of a MARC cell expression library was performed. Moreover, this is the first report of the RNA binding property of a tetraspan molecule, Platelet Endothelial Tetraspan Antigen-3 (PETA-3), also designated as CD 151, and its role in PRRS virus infection. It is known that viruses bind to receptors (protein-protein interaction) and get into the cell in endosome. Under low pH conditions, the virus undergoes structural disorganization and releases viral RNA into the endosome. However, the method of entry of viral RNA in endosome into cell cytoplasm is not known. The present invention demonstrates that RNA binding proteins, such as CD 151, help PRRSV to enter into cell cytoplasm for further replication of the virus (FIG. 9).

[0035] The present invention also determined the mRNA sequence for porcine CD 151 and this sequence is provided herein as SEQ ID No. 38. For purposes of the present invention, it is preferred to use mRNA sequences which corresponds to a DNA sequence having at least 84% sequence homology with SEQ ID No 0.38. More preferably, the DNA sequence will have at least 90% and still more preferably at least 95% and most preferably at least 98% sequence homology with SEQ ID No. 38.

[0036] The present invention also provides the DNA sequence coding for CD 151. When using DNA sequences coding for CD 151 which are non-simian in origin, it is preferred that such sequences are derived from porcine CD 151 and have at least 84% sequence homology with SEQ ID No. 14. More preferably, the DNA sequence will have at least 90%, more preferably at least 95%, and most preferably at least 98% sequence homology with SEQ ID No. 14. The genomic sequence of porcine CD 151 is the combination of introns and exons summarized in Table 2. As noted above, the exons share 84% or less sequence homology with other known CD 151 sequences and the introns share no homology with any known sequences. Accordingly, when it is desired to construct or use a CD 151 sequence of non-simian origin, the DNA sequence is preferred to have at least one of the introns have at least 84% sequence homology with a sequence selected from the group consisting of SEQ ID Nos. 16, 18, 21, 23, 25, 27 and 29. Similarly, the DNA sequence is preferred to have at least one of the exons with at least 84% sequence homology with a sequence selected from the group consisting of SEQ ID Nos. 15, 17, 19, 20, 22, 24, 26, and 28.

[0037] In another aspect of the present invention, a vaccine for inducing effective immunity against PRRSV is provided. The vaccine comprises viral progeny produced in a non-simian cell line transformed with non-simian CD 151. Preferably, the CD 151 is of porcine origin. Still more preferably, the CD 151 will have at least 84% sequence homology with SEQ ID No. 14.

[0038] In another aspect of the present invention, a method of determining the effect of single nucleotide polymorphisms on PRRSV susceptibility is provided. The method generally comprises the steps of obtaining at least two CD 151 genomic sequences, comparing single nucleotide polymorphisms between the sequences, and correlating the single nucleotide polymorphisms with susceptibility to PRRSV.

[0039] Finally, the present invention provides a method of comparing PRRSV susceptibility factors between individual swine, the method generally comprises the steps of obtaining the genetic sequence of at least two swine, analyzing the amount of CD 151 encoding sequences, and comparing the amount of CD 151 encoding sequences. The genetic sequence of the swine can be obtained from a biopsy from an ear notch or tail snip, and performing PCR on the biopsy to determine CD 151 sequences. Information obtained using such method can also be used to correlate expression levels with susceptibility to PRRSV.

BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The file of this patent contains at least one drawing executed in color. Copies of this patent with color drawing(s) will be provided by the Patent and Trademark Office upon request and payment of the necessary fee.

[0041]FIG. 1 is the nucleotide sequence of the simian CD 151 cDNA clone, and the predicted amino acid sequence wherein the putative transmembrane domains are underlined and the inframe stop codon is indicated by an asterisk;

[0042]FIG. 2 is a photograph of the RNA-binding activity of the CD 151 protein detected by immunoprecipitation with CD 151 mAb in a Northwestern blotting assay;

[0043]FIG. 3 is a photograph of the RNA binding activity of the CD 151 protein detected by immunoprecipitation with β-galactocidase mAb in a Northwestern blotting assay;

[0044]FIG. 4 is a photograph of the in vivo RNA binding activity of the CD 151 protein, as demonstrated by RT-PCR after immunoprecipitation of PRRSV infected MARC cell lysates;

[0045]FIG. 5 is a photograph of the RT-PCR result illustrating the amplification of the CD 151 105 bp amplicon;

[0046]FIG. 6 is a photograph of the results of a western blotting experiment detecting the presence of CD 151;

[0047]FIG. 7a is a photograph of immunohistochemistry staining to detect the presence of PRRSV in wild-type BHK-21 cells showing no detection of PRRSV antigen;

[0048]FIG. 7b is a photograph of immunohistochemistry staining to detect the presence of PRRSV in BHK-21 cells which have been transfected with CD 151;

[0049]FIG. 8 is a graph illustrating the enhanced PRRSV production by MARC cells after stable transfection with CD 151;

[0050]FIG. 9 is a schematic representation of the mechanism of PRRS viral RNA entry into a target cell and the role of RNA-binding proteins such as CD 151;

[0051]FIG. 10 is a schematic representation of the sequence of porcine CD 151 DNA; and

[0052]FIG. 11 is a photograph of a northwestern blot illustrating the RNA binding activity of porcine CD 151.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0053] The following examples set forth preferred embodiments of the present invention. It is to be understood, however, that these examples are provided by way of illustration and nothing therein should be taken as a limitation upon the overall scope of the invention.

[0054] As used herein, the following definitions will apply: “Sequence Identity” as it is known in the art refers to a relationship between two or more polypeptide sequences or two or more polynucleotide sequences, namely a reference sequence and a given sequence to be compared with the reference sequence. Sequence identity is determined by comparing the given sequence to the reference sequence after the sequences have been optimally aligned to produce the highest degree of sequence similarity, as determined by the match between strings of such sequences. Upon such alignment, sequence identity is ascertained on a position-by-position basis, e.g., the sequences are “identical” at a particular position if at that position, the nucleotides or amino acid residues are identical. The total number of such position identities is then divided by the total number of nucleotides or residues in the reference sequence to give % sequence identity. Sequence identity can be readily calculated by known methods, including but not limited to, those described in Computational Molecular Biology, Lesk, A. N., ed., Oxford University Press, New York (1988), Biocomputing: Informatics and Genome Projects, Smith, D. W., ed., Academic Press, New York (1993); Computer Analysis of Sequence Data, Part I, Griffin, A. M., and Griffin, H. G., eds., Humana Press, New Jersey (1994); Sequence Analysis in Molecular Biology, von Heinge, G., Academic Press (1987); Sequence Analysis Primer, Gribskov, M. and Devereux, J., eds., M. Stockton Press, New York (1991); and Carillo, H., and Lipman, D., SIAM J. Applied Math., 48: 1073 (1988), the teachings of which are incorporated herein by reference. Preferred methods to determine the sequence identity are designed to give the largest match between the sequences tested. Methods to determine sequence identity are codified in publicly available computer programs which determine sequence identity between given sequences. Examples of such programs include, but are not limited to, the GCG program package (Devereux, J., et al., Nucleic Acids Research, 12(1):387 (1984)), BLASTP, BLASTN and FASTA (Altschul, S. F. et al., J. Molec. Biol., 215:403-410(1990). The BLASTX program is publicly available from NCBI and other sources (BLAST Manual, Altschul, S. et al., NCVI NLM NIH Bethesda, Md. 20894, Altschul, S. F. et al., J. Molec. Biol., 215:403-410 (1990), the teachings of which are incorporated herein by reference). These programs optimally align sequences using default gap weights in order to produce the highest level of sequence identity between the given and reference sequences. As an illustration, by a polynucleotide having a nucleotide sequence having at least, for example, 95% “sequence identity” to a reference nucleotide sequence, it is intended that the nucleotide sequence of the given polynucleotide is identical to the reference sequence except that the given polynucleotide sequence may include up to 5 point mutations per each 100 nucleotides of the reference nucleotide sequence. In other words, in a polynucleotide having a nucleotide sequence having at least 95% identity relative to the reference nucleotide sequence, up to 5% of the nucleotides in the reference sequence may be deleted or substituted with another nucleotide, or a number of nucleotides up to 5% of the total nucleotides in the reference sequence may be inserted into the reference sequence. These mutations of the reference sequence may occur at the 5′ or 3′ terminal positions of the reference nucleotide sequence or anywhere between those terminal positions, interspersed either individually among nucleotides in the reference sequence or in one or more contiguous groups within the reference sequence. Analogously, by a polypeptide having a given amino acid sequence having at least, for example, 95% sequence identity to a reference amino acid sequence, it is intended that the given amino acid sequence of the polypeptide is identical to the reference sequence except that the given polypeptide sequence may include up to 5 amino acid alterations per each 100 amino acids of the reference amino acid sequence. In other words, to obtain a given polypeptide sequence having at least 95% sequence identity with a reference amino acid sequence, up to 5% of the amino acid residues in the reference sequence may be deleted or substituted with another amino acid, or a number of amino acids up to 5% of the total number of amino acid residues in the reference sequence may be inserted into the reference sequence. These alterations of the reference sequence may occur at the amino or the carboxy terminal positions of the reference amino acid sequence or anywhere between those terminal positions, interspersed either individually among residues in the reference sequence or in the one or more contiguous groups within the reference sequence. Preferably, residue positions which are not identical differ by conservative amino acid substitutions. However, conservative substitutions are not included as a match when determining sequence identity.

[0055] Similarly, “sequence homology”, as used herein, also refers to a method of determining the relatedness of two sequences. To determine sequence homology, two or more sequences are optimally aligned as described above, and gaps are introduced if necessary. However, in contrast to “sequence identity”, conservative amino acid substitutions are counted as a match when determining sequence homology. In other words, to obtain a polypeptide or polynucleotide having 95% sequence homology with a reference sequence, 95% of the amino acid residues or nucleotides in the reference sequence must match or comprise a conservative substitution with another amino acid or nucleotide, or a number of amino acids or nucleotides up to 5% of the total amino acid residues or nucleotides, not including conservative substitutions, in the reference sequence may be inserted into the reference sequence.

[0056] A “conservative substitution” refers to the substitution of an amino acid residue or nucleotide with another amino acid residue or nucleotide having similar characteristics or properties including size, hydrophobicity, etc., such that the overall functionality does not change significantly.

[0057] Isolated” means altered “by the hand of man” from its natural state., i.e., if it occurs in nature, it has been changed or removed from its original environment, or both. For example, a polynucleotide or polypeptide naturally present in a living organism is not “isolated,” but the same polynucleotide or polypeptide separated from the coexisting materials of its natural state is “isolated”, as the term is employed herein.

[0058] “Cellular material” refers to cells, tissues, and fluids containing material of cellular origin.

[0059] “Anti RNA Entry Proteins” or Anti REPs” refer to a novel class of chemicals or chemical analogues that prevent binding of the viral RNA, with an RNA protein. These Anti REPs are nontoxic to mammalian cells but are able to prevent infection of cells from RNA viruses.

EXAMPLE 1

[0060] This example identifies and describes the cells, virus and monoclonal antibodies used in later experiments, prepares the λ Zap expression library, details the cloning and probe preparation of the 3′UTR of the PRRSV genome, describes the screening of the cDNA library for cells containing CD 151, describes the transfection of cells with plasmid containing CD 151, and verifies that the transfection was successful and that CD 151 binds to the 3′UTR of PRRS virus.

[0061] Materials and Methods:

[0062] The MARC, COS-7, Vero, CL 2621, MA-104 (derivatives of African green monkey kidney cells) and BHK-21 (Baby hamster kidney) cell lines were used in the study. The MARC cells were grown in Eagle's minimum essential medium (MEM) (Life Technologies, Inc., Gaithersburg, Md.) supplemented with 10% fetal calf serum (FCS; Hyclone, Logan, Utah). Dulbecco's minimum essential medium (Life Technologies, Inc., Gaithersburg, Md.) with 10% FCS was used to cultivate BHK-21 cells. The ATCC VR 2332 strain of PRRS virus was used in the study. Unless otherwise stated, the virus was propagated in MARC cells. The anti-CD 151 monoclonal antibody (MAb) clone 14A2.H1 was purchased from Pharmingen International, San Diego, Calif. The anti-β-galactosidase MAb clone D19-2F3-2 (Boehringer Mannheim, Indianapolis, Ind.) and the anti-PRRSV nucleoprotein MAb, SR 30 (Rural Technologies, Brookings, S. Dak.), were used in the study.

[0063] To prepare the λ Zap expression library, the MARC cell line cDNA library was prepared using a ZAP Express cDNA synthesis kit (Stratagene, La Jolla, Calif.) following the manufacturer's instructions. Total cellular RNA was extracted from the cells by the acid phenol-guanidinium isothiocyanate method. The mRNA was isolated from total cellular RNA using an oligo(dT) cellulose column (Stratagene, La Jolla, Calif.), and then 5 μg of mRNA was converted to cDNA and cloned directionally in the λ ZAP Express vector. The cDNA library was packaged using the ZAP Express cDNA Gigapack III Gold cloning kit (Stratagene, La Jolla, Calif.). The quality of the library was verified by blue/white screening and also by confirming the size of the insert.

[0064] To clone the 3′UTR of PRRSV genome and prepare a probe, the 3′UTR was cloned into the pCR II vector by RT-PCR amplification of the PRRSV RNA by TA cloning using the forward primer 5′-CCCCATTTTCCTCTAGCGACTG-3′ (SEQ ID No. 31) and the reverse primer 5′-CGGCCGCATGGTTCTCGCCAAT-3′ (SEQ ID No. 32). The [α-³²P]UTP RNA transcript was prepared by in vitro transcription. The cDNA was linearized by digestion with BamHI and then transcribed in vitro using a Riboscribe™ (Epicentre Technologies, Madison, Wis.) T7 RNA synthesis kit and following the manufacturer's instructions. The DNA template was digested with 1 MBU of RNase-free DNase for 15 minutes at 37° C. Quick Spin™ columns (Boehringer Mannheim, Indianapolis, Ind.) were used to remove free nucleotides. The probe was precipitated using 0.3 M sodium acetate and 2.5 volumes of 100% ethanol at −20° C. for 30 minutes. The activity of the probe was measured with a radioactive counter (Bioscane, Inc., Washington, D.C.).

[0065] Next, the cDNA library was screened by Northwestern blotting as previously described with slight modifications. In all the rounds of screening, plaques were induced for 1.5 hours during the first lift and 2 hours for the second with 10 mM IPTG. Nitrocellulose membranes from plaque lifts were denatured in 6 M guanidinium hydrochloride for 30 minutes and gradually renatured with equal changes of single binding buffer (SB Buffer: 15 mM HEPES [pH 7.9]; 50 mM KCl, 0.01% [v/v] Nonidet P-40; 0.1% [w/v] Ficoll 400-DL; 0.1% [w/v] PVP-40; 0.1 mM MnCl_(2;) 0.1 mM ZnCl_(2;) 0.1 mM EDTA; 0.5 mM DTT) every 10 minutes. During prehybridization and hybridization 250 μl of ssDNA and 5 μl (10 mg/ml) of yeast tRNA were added to 5 ml of SB buffer to block non-specific binding. Hybridization was performed overnight with the 3′ UTR PRRSV [³²P]RNA probe at 500,000 cpm/ml. RNA binding activity was detected by autoradiography.

[0066] The corresponding positive plaques were cored and eluted in 1 ml of SM buffer with 40 μl chloroform. The inserts were excised using the Gigapack III gold cloning kit. The insert, now in the pBK-CMV vector, was sequenced manually with T7 and T3 primers using a Sequitherm EXCEL II DNA sequencing kit (Epicentre Technologies, Madison Wis.). Sequencing was also performed at the Iowa State University Sequencing Facility in Ames, Iowa. A BLAST homology search was carried out to identify similar proteins.

[0067] To transfect the BHK-21 and MARC cell lines, pBK-CMV plasmid containing CD 151 gene using Lipofectamine reagent following manufacturer's instructions (Life Technologies, Inc., Gaithersburg, Md.) was used. For transient transfection, cells were harvested 24 hours after transfection. Stable transfection was done by G418 (Omega Scientific, Inc., Tarzana, Calif.) selection in growth medium at a concentration of 1 mg/ml for BHK-21 cells and 0.7 mg/ml for MARC cells. After selection, cells were maintained in the presence of G418 at 0.5 mg/ml for BHK-21 cells and 0.35 mg/ml for MARC cells. The expression of CD 151 was measured by immunoprecipitation.

[0068] Next, to demonstrate that CD 151 binds to the 3′UTR of PRRS virus, a Northwestern blot of the immunoprecipitated CD 151 protein was performed. Transfected cells in 24 well plates were lysed in 100 μl of single detergent lysis buffer (50 mM Tris-HCl [pH 8], 150 mM NaCl, PMSF 100 μg/ml and 1% [v/v] NP-40). To 50 μl of cell lysate, 1 μl of Mab (anti-CD 151 and anti-β-galactosidase antibodies) was added and rocked overnight at 4° C. Immunocomplexes were precipitated on ice for 2 h with addition of 4 μl of formalin-fixed S. aureus cells and centrifuged at 4,000×g for 10 minutes. All subsequent washes were done by centrifugation at 12,000×g for 10 minutes. The pellet was washed once in cold TSA (0.05 M Tris-HCl [pH 8.0]; 0.15 M NaCl; 0.025% NaN₃), 1% Triton X-100 and 1% SDS. The second wash was done in cold TSA alone followed by two washes in 10 mM Tris-HCl [pH 7.5] containing 1 mM EDTA. The pellet was suspended in 20 μl of 2×SDS loading buffer and electrophoresized on a 10% SDS-PAGE gel. The proteins were blotted on nitrocellulose membrane and the Northwestern blot was carried out as described above.

[0069] Results:

[0070] In order to identify the MARC cell proteins binding to 3′UTR RNA of PRRSV, a cDNA library of MARC cells was made and screened by Northwestern blotting using radiolabelled 3′UTR. The MARC cell cDNA library had a titer of 10⁸ plaque forming units (pfu) with an average insert size of 1-4 kb (Data not shown). Approximately 6×10⁶ plaques were screened by Northwestern blotting. The single reacting clone was obtained by repeated plaque purification and rescreening five times. In the last round of screening, a single isolated plaque was cored and excised. On restriction digestion, the size of the insert was found to be 1.5 kb (data not shown). After manual sequencing, a BLAST search showed that the insert had 98% homology with CD 151/PETA-3, a tetraspan molecule. Sequencing of the complete insert was also performed at the Iowa State University Sequencing Facility in Ames, Iowa. The insert was a full-length cDNA with start and stop codons and also a poly (A) tail. This is the first report of the complete sequence of a simian CD 151 gene. The sequence (Genbank accession number, AF275666) is shown in FIG. 1 with the putative transmembrane region underlined. Although the sequence provided is simian, it is believed that CD 151 sequences isolated from other animal lines (e.g. swine) could also be used due to their predicted homology with this simian CD 151 sequence. The presence of porcine CD 151 in alveolar macrophages has been proven by Western Blot (see FIG. 5).

[0071] Immunoprecipitation followed by Northwestern blotting was carried out to validate the observation that CD 151 has RNA binding activity. Both BHK-21 and MARC cells were transfected with the pBK-CMV plasmid containing the CD 151 insert (obtained by library screening). Since CD 151 was to be expressed as a lac Z fusion protein, the transfected cell lysate was immunoprecipitated with both anti-CD 151 and anti-β-galactosidase MAbs. The protein immunoprecipitated with both MAbs exhibited RNA binding activity when probed with 3′ UTR PRRSV [³²P]RNA as shown in FIGS. 2 and 3 while the controls were negative. This proves that the expressed protein, which is CD 151, has PRRSV RNA binding activity and that it binds to the 3′ UTR of PRRSV. In FIG. 2, lane 1 contained the MARC lysate (without immunoprecipitation), lane 2 contained transfected MARC cells, lane 3 contained transfected BHK-21 cells, lane 4 contained untransfected MARC cells, and lane 5 contained untransfected BHK-21 cells. For FIG. 3, lane 1 contained untransfected BHK-21 cells, lane 2 contained transfected BHK-21 cells, lane 3 contained transfected MARC cells, lane 4 contained untransfected MARC cells, and lane 5 of FIG. 3 is the MARC cell lysate(without immunoprecipitation).

EXAMPLE 2

[0072] This example determined that CD 151 expression by BHK-21 cells rendered the cells susceptible to PRRS infection.

[0073] Materials and Methods:

[0074] To determine whether BHK-21 cells expressing CD 151 (obtained by stable transfection) become susceptible to PRRSV infection, immunohistochemical staining was performed. Cells were seeded in 24 well plates and infected with PRRSV at a multiplicity of infection (MOI) of 0.01 at 37° C. for 1 hour. Infectivity was determined by immunohistochemistry 24-hours post infection. Cells were fixed in acetone-PBS (3:1, v/v) for 10 minutes at 4° C. and air-dried for 5 minutes. The primary antibody, anti-PRRSV nucleoprotein MAb (1:1000 dilution in PBS) was added and incubated for 1 hour at 37° C. Cells were then washed once in PBS for 10 minutes and incubated with anti-mouse IgG biotinylated antibody (Vector Labs, Burlingame, Calif.) for 30 minutes at room temperature (RT). After washing once in PBS for 10 minutes, avidin-biotin enzyme complex (Vector Labs) was added and incubated for 30 minutes at RT. The cells were then washed once in PBS for 10 minutes, once in distilled water for 5 minutes, then DAB substrate was added and incubated in the dark for 10 minutes. The cells were washed in distilled water for 5 minutes, counterstained with Gill's-1 hematoxylin for 30 seconds, washed in tap water, then examined by light microscopy.

[0075] Results:

[0076] The results for this example are given in FIGS. 7a and 7 b. The parent BHK-21 cell line pictured in FIG. 7a was not susceptible to PRRSV but recombinant CD 151-transformed BHK-21 cells pictured in FIG. 7b were positive for the PRRSV antigen, thereby indicating susceptibility to PRRSV infection. Thus, the introduction of CD 151 rendered a previously unsusceptible simian cell line susceptible to PRRSV infection. As shown in FIG. 2, untransfected MARC cells contain CD 151 while untransfected BHK-21 do not contain CD 151. Interestingly, untransfected MARC cells are susceptible to PRRSV infection while untransfected BHK-21 cells are not.

EXAMPLE 3

[0077] This example utilized a virus burst assay to assess the effects of MARC cells which overexpress CD 151.

[0078] Materials and Methods:

[0079] The monolayer of MARC cells overexpressing CD 151 (obtained by stable transfection as described in Example 1) was infected with PRRSV at a MOI of 0.1 at 37° C. for 1 hour. Cells were washed twice in MEM and overlaid with 1 ml of MEM supplemented with 1% FCS. After incubating for 18 hours, cells were lysed by freeze thawing and cell debris was removed by centrifugation at 12,000×g for 5 minutes. The amount of virus in the supernatant was titrated by plaque assay using parent MARC cells. To determine if there are any effects of overexpression of CD 151 on PRRSV replication, MARC cells were examined with respect to the effect on infectivity level. The MARC cells (both parent and transfected progeny cell line overexpressing CD 151) were infected with equal amounts of plaque purified PRRSV and allowed to grow for one complete replication cycle (18 hours). The level of PRRSV was measured by plaque assay using parent MARC cells. In plaque assay, 100 μl of serial dilutions (10-fold) of the supernatant were used for infection as described above. After infection, the monolayer was washed once in PBS and once in MEM, then overlaid with 1 ml MEM containing 1% FCS and 1% agar. Plaques were visualized after 1 day of incubation at 37° C. by staining with 0.01% neutral red.

[0080] Results:

[0081] There was an approximately 100-fold increase in the amount of virus in transfected MARC cells overexpressing CD 151 as compared to parent MARC cells and these results are given in FIG. 8. When these results are taken in combination with the results from the previous experiment on viral entry, it is believed that CD 151 may have increased the levels of PRRSV infection by promoting viral RNA or viral entry. Thus, introduction of CD 151 can be used to produce higher titer stocks of PRRSV. Similarly, determining the amount or expression of CD 151 in a particular swine will give an indication as to their susceptibility to PRRS infection, in comparison to a standard. In this manner, a large number of samples from different tissues and fluids will be assayed for their CD 151 levels in order to establish an average or standard for that tissue or fluid. Individual levels of CD 151 obtained from the same tissue or fluid can then be compared to this average or standard in order to determine an individual animal's susceptibility to PRRS infection.

EXAMPLE 4

[0082] This example utilized RT-PCR to detect CD 151 mRNA in MARC cells.

[0083] Materials and Methods:

[0084] RNA was extracted from the PRRSV infected MARC cells using the acid phenol-guanidinium isothiocyanate method. RNA quality was evaluated by agarose gel electrophoresis. RT-PCR was performed using the GeneAmp RNA PCR kit (Perkin Elmer, Foster City, Calif.) with forward 5′-CCTACCTGGCCACAGCCTAC-′3 (SEQ ID No 33) and reverse 5′-ACAGGCGCAGCAGGTTCCGA-′3 (SEQ ID No 34) primers. The reverse transcription reaction was performed at 42° C. for 45 minutes, 95° C. for 10 minutes and 5° C. for 5 minutes. PCR was done at 94° C. for 2 minutes, 94° C. for 30 sec, 55° C. for 30 sec, 72° C. for 15 sec, for 25 cycles and 72° C. for 30 minutes. The products were analyzed in 2% agarose gels stained with ethidium bromide.

[0085] Results:

[0086] A predicted RT-PCR result showing the amplification of the 149 bp amplicon is shown in FIG. 4. In this figure, the in vivo binding activity of CD 151 protein was demonstrated by RT-PCR after immunoprecipitation with CD 151 MAb of infected MARC cell lysates. In this figure, lane M is a 123 bp ladder, lane 1 is the PCR -ve control, lane 2 is the uninfected but immunoprecipitated MARC cell line, lane 3 is the infected immunoprecipitated with unrelated wasp (Cotesia folepis) MAb, lane 4 is the infected MARC cells immunoprecipitated with CD 151 MAb with no UV-crosslinking CL 2621 cell line; lane 5 is the infected MARC cells immunoprecipitated with CD 151 MAb after 15 minutes of UV crosslinking, lane 6 is the infected MARC cells immunoprecipitated with CD 151 MAb after 30 minutes of UV crosslinking, and lane 7 is the infected MARC cells immunoprecipitated with CD 151 MAb after 45 minutes of UV crosslinking.

EXAMPLE 5

[0087] This example determined if CD 151 possessed in vivo RNA binding activity by utilizing in vivo cross-linking.

[0088] Materials and Methods:

[0089] MARC cell monolayers in 24 well plates were infected with PRRSV at a MOI of 0.1 at 37° C. for 1 hour. The monolayer was washed 3 times in PBS, twice in MEM, and replaced with MEM supplemented with 1% FCS. Eighteen hours post infection, the cells were washed twice in PBS then covered in fresh PBS and held on ice in a UV cross linker (Fisher Scientific, Pittsburgh, Pa.) at a distance of 10 cm from the 300 λ light source to be irradiated for 15, 30, and 45 minutes. After irradiation, the PBS was removed and the cells were lysed by addition of 50 μl of single detergent lysis buffer then freeze thawed. Immunoprecipitation was performed as described above using anti-CD 151 MAb except that IgG coupled sepharose beads were used instead of formalin-fixed S. aureus cells. Proteineous material was digested with Proteinase-K (4 μg/ml) for 15 minutes at 37° C. and RNA was extracted using the phenol-guanidinium method. RT-PCR was performed to determine the presence of PRRSV RNA using forward (SEQ ID No 35) forward 5′TGGGCTGGCATTCTTGAGGC′3 and (SEQ ID No 36) reverse 5′TTCGGGCCGCATGGTTCTCGC′3 primers.

[0090] Results:

[0091] UV cross-linking followed by RT-PCR was performed to determine if CD 151 possesses in vivo RNA binding activity. The rationale was that if there was any interaction between the CD 151 protein and the 3′ UTR RNA of PRRSV inside the cell, the complex should immunopreciptiate with the addition of anti-CD 151 MAb. The MARC cells were infected with PRRSV and to strengthen the interaction between 3′ UTR RNA of PRRSV and CD 151, UV cross-linking was performed as described in the methods. Immunoprecipitated complex was treated with proteinase K to remove the proteinaceous material. The 3′ UTR RNA of PRRSV was detected in the immunoprecipitate by RT-PCR as shown in FIG. 4. The interaction between the CD 151 protein and the 3′ UTR of PRRSV was strong and 15 minutes of UV-induced cross-linking was sufficient to immunoprecipitate RNA along with CD 151 while the control with non-specific MAb was negative. Thus, CD 151 does possess in vivo RNA binding activity.

EXAMPLE 6

[0092] This example utilized western blotting to detect the CD 151 in MARC, BHK-21, and Vero cell proteins.

[0093] Materials and Methods:

[0094] MARC, BHK-21 and VERO cell proteins were electrophoresed in 10% SDS-PAGE gel and blotted onto a nitrocellulose membrane. After blocking overnight in 5% non-fat dried milk in PBS, the membrane was incubated in anti-CD 151 MAb (1:2,000 in PBS-T) at room temperature for 5 hours. The membranes were washed in PBS-T for 15 minutes twice and incubated in anti-mouse HRPO conjugate (1:10,000) for 2 hours at room temperature. After washing, the proteins were detected by 3, 3′, 5, 5′-tetra-methylbenzidine (TMB) membrane peroxidase substrate following manufacturer's instructions (Kirkegaard and Perry Laboratories, Gaithersburg, Md.).

[0095] Results:

[0096] The presence of CD 151 in susceptible cells was determined by western blotting using anti-CD 151 MAb. As shown in FIGS. 5 and 6, the susceptible MARC cells have CD 151 protein while the non-susceptible BHK-21 cells lack the protein. Moreover, transfected BHK-21 cells (FIG. 5, lane 13) do have CD 151 and are susceptible to PRRSV infection. There has been no report of susceptibility of COS-7 cells for PRRSV, while in Vero cells, the PRRSV enters the cells but does not result in productive viral infection. The Vero cells might lack other cellular factors required for PRRSV infection. These results indicate that CD 151 is one of the factors in determining the susceptibility to PRRSV infection with possible involvement of additional intracellular factors.

EXAMPLE 7

[0097] This example determined the correlation between the presence of CD 151 and susceptibility to PRRSV infection.

[0098] Materials and Methods:

[0099] To determine the possible relationship between the presence of CD 151 and susceptibility of to PRRSV infection, RT-PCR using CD 151 specific primers was performed to screen susceptible and non-susceptible cell lines. These cell lines included MA 104, MARC, Vero, COS-7, the three of which are all derived from African green monkey cells, ST, BHK-21, MDBK and HRT (Human rectal tumor cells) cell lines. Total RNA was extracted as described in Example 4 and the presence of CD 151 was detected by RT-PCR using the procedures and primers described in Example 4.

[0100] Results:

[0101] In MA 104, MARC 145, Vero, COS-7, and ST cell lines there was a 105 bp amplicon which was of the expected size. There were additional higher bands in CL2621, Vero, and COS-7 cell lines that could be due to the presence of alternate spliced forms of CD 151. The CD 151 was absent in BHK-21, MDBK (See FIG. 5) and HRT cell lines. Interestingly MARC 145, MA 104, and CL2621 are the cell lines susceptible to PRRSV infection while BHK-21 cell lines are non-susceptible. In the past, is was believed that the only cells that were susceptible to PRRSV were the simian cell lines CL-2621 and MARC-145 swine alveolar macrophages. Thus, the present invention refutes the previous claim that only simian cell lines are susceptible to PRRSV (see U.S. Pat. No. 5,846,805) because after transfection with CD 151, which is an accessory factor, non-simian cell lines are susceptible to PRRS virus. The BHK-21, MA 104, COS-7, ST, MDBK, and HRT 18 cell lines are available from the American Type Culture Collection (ATCC), 12301 Parklawn Drive, Rockville, Md. 20852. The representative accession numbers are: BHK-21 is ATCC # CRL8544; MA104 is ATCC# CRL2378; COS-7 is ATCC# CRL1651; ST is ATCC# CRL1746; MDBK is ATCC# CCL22; and HRT18 is ATCC# CCL244. The MARC 145 cell line was obtained from National Veterinary Sciences Laboratory (NVSL) in Ames, Iowa and CL2621 is a proprietary cell line obtained from NVSL, Ames, Iowa. The Vero cell line has been accorded ATCC # CCL81. Thus, this example provides further evidence that CD 151 plays an important role in PRRSV infection.

EXAMPLE 8

[0102] This example determined the lack of direct protein-protein interaction between CD 151 protein and PRRSV proteins, thereby proving that CD 151 is an accessory protein but not a PRRSV viral receptor.

[0103] Materials and Methods:

[0104] After establishing that CD 151 is essential for PRRSV infection, the potential for direct interaction between the PRRSV proteins and CD 151 was determined by coimmunoprecipitation. The infected MARC cells were immunoprecipitated with CD 151 MAb and the presence of PRRSV proteins in the immunoprecipitate was detected by PRRSV polyclonal antibody as the primary antibody and anti-swine HRPO as the secondary antibody followed by detection with the ECL western blot detection system (Amersham Pharmacea Biotech, Piscataway, N.J.). The coimmunoprecipitation was also performed by first immunoprecipitating with PRRSV polyclonal antibody and checking for the presence of CD 151 in the immunoprecipitate by CD 151 monoclonal antibody as the primary antibody and anti-mouse HRPO as the secondary antibody.

[0105] Results:

[0106] There was no direct interaction between the CD 151 and PRRSV viral protein. This eliminates the possibility of CD 151 as a receptor. However, it does not rule out the possibility of an indirect interaction between CD 151 and PRRS viral protein. The indirect interaction will involve identification of yet another protein that could fit and complete the interaction between CD 151 and PRRS viral protein. Thus, viral RNA-protein interaction has been validated but there is no direct protein-protein interaction between CD 151 and PRRSV viral proteins. Accordingly, CD 151 is an accessory protein but not a receptor protein because it enhances PRRSV titers, and thus enhances and mediates the entry of viral RNA.

EXAMPLE 9

[0107] This example reviews the methods used to discover chemical compounds used to stop the interaction between viral RNA and CD 151 and provide for a novel class of anti-viral compounds called anti-RNA entry proteins.

[0108] Materials and Methods:

[0109] Based on this invention it appears that entry of viral RNA into the cell is mediated by the interaction of the viral RNA with the RNA-binding protein. This test can be carried out easily in vitro. In a high-throughput system, the motif of the CD 151 or the full-length CD 151 can be spotted with an automatic instrument on nitrocellulose or in any solid-binding matrix. In a negative control, where no drug is present, the binding aptamer of RNA in the form of a ssDNA can be fluorescently labeled and subsequently added in a well. If no drug is present, a maximum level (100%) of fluorescence or binding activity will be observed. A wide variety of unknown chemicals can be added to the plate. The compounds that block the binding of the oligonucleotide with the RNA-binding aptamer will be further modified to find some effective non-toxic compounds that could be used to block the entry of PRRSV RNA in the cells. Similar principles can be used for the discovery of treatments for a wide variety of animal viruses. It is believed that this novel class of pharmaceuticals has not been described in the literature.

[0110] Alternatively, with the discovery of yeast hybrid systems 3′ UTR RNA of PRRSV and CD 151 protein can be adapted to the yeast tri-hybrid system for discovery of compounds that will block their interaction.

EXAMPLE 10

[0111] This example shows a non-invasive method for the utilization of the present invention in screening live pigs and stored germplasm for CD 151 mRNA and levels of susceptibility of possible progeny to PRRSV. Additionally, this Example is similar to Example 4 and illustrates applications of this invention in screening live pigs boar semen and extends the application of the present invention to subsequent litters in future generations in swine breeding programs for improved swine resistance to PRRS virus.

[0112] Materials and Methods:

[0113] On the basis of this invention, it is clear that the level of CD 151 is a critical factor in determination of the susceptibility of the target cell to PRRSV. Different breeding lines of pigs will be screened by quantitative RT-PCR for the level of CD 151 in cellular material such as alveolar macrophages, semen, germ cells, ova, and platelets. The lines of pigs having lower levels of CD 151 in target organs are expected to be less susceptible to PRRS and are thus less affected by the harmful effects of PRRS infection. Currently, pigs are selected on the basis of sacrificing after infection and are mated. The animals found to carry relatively less amounts of CD 151 will be selectively mated against PRRS susceptibility. This will allow a non-invasive method of checking the animals. With the help of CD 151 knockout experiments, it will be possible to develop a pig line that is completely resistant to PRRS virus infection.

[0114] Results:

[0115] This example demonstrates that the present invention overcomes the current limitation of sacrificing different lines of pigs for determining their susceptibility after experimental infection with PRRSV. Using non-invasive diagnostic methods such as peripheral blood platelets, stored germplasm, or extended and non-extended porcine germplasm, swine breeding operations should be able to select for animals that have reduced susceptibility to PRRSV infection.

EXAMPLE 11

[0116] This example permits quantification of CD 151 levels in different swine breeding lines.

[0117] Materials and Methods:

[0118] This Example is similar to Example 4 except that the plasmid pKSU is used for quantitative purposes. This plasmid contains full-length open reading frames of CD 151. A known amount of this plasmid (e.g. 0.05 micrograms) is introduced into the PCR tubes and known dilutions of the predetermined sample will be added to cover the range of the expected CD 151 levels in different swine tissues, thereby providing known prequantified standards. The amount of CD 151 in unknown swine samples will be quantified by comparison with the known standard curve. Additionally, to find the precise amount of CD 151 in swine tissues, a quantitative TaqMan for CD 151 can be performed. This will provide precise quantification of CD 151 in germplasm and peripheral blood platelets in picogram to nanogram amounts per milliliter or per gram of known swine tissue, per milliliter of germplasm, or per one million swine platelets or per one million swine spermatazoa.

[0119] Results:

[0120] By quantitative CD 151 RT-PCR, swine breeding lines lower in CD 151 will be selected for breeding for reduced PRRSV susceptibility.

EXAMPLE 12

[0121] This example illustrates the use of non-simian, recombinant cell lines for production of higher titer, safer swine vaccines to control or prevent PRRSV.

[0122] Materials and Methods:

[0123] Based on this invention, non-simian cell lines transformed with CD 151 are not only susceptible to PRRSV but propagate the PRRS virus to much higher titers than parent cell lines. First, the cell lines will be checked for contaminations such as Mycoplasma, porcine parvovirus, and BVD virus using methods that are well known in the art. Once the cell line has been found to be free of these contaminates, the cell line will be plated in flasks or roller bottles and will be infected with plaque purified PRRS virus. The American isolate, Lelystad virus, or any other PRRS virus isolate can be used. The cell cultures will be infected for sixty hours after which they will be frozen at −80° C., and freeze-thawed 3 times. Cellular material will be removed and clear supernatant will be used as a vaccine after titration. It is recommended to use 1 million PFUs/ml and the dose of the vaccine will be 1 ml intramuscularly in the presence of the parenteral adjuvants. This vaccine can even be diluted because of its high titer for making specific doses per vial. Alternatively, various combinations that are known in this field of art can be applied. All manipulations and modifications included in this invention are routine in the field of preparation of biologics for animal vaccines.

[0124] Results:

[0125] The preceding materials and methods produce a safe, high titer killed or modified-live virus vaccine for PRRSV in non-simian cell lines.

EXAMPLE 13

[0126] This example shows the application of non-simian cell lines for propagation of PRRSV for development of in vitro diagnostic assays.

[0127] Materials and Methods:

[0128] Advantageously, non-simian cell lines can be used for propagating PRRSV because of their higher susceptibility for propagating the wild type virus from clinical samples such as nasal swabs and tissues such as lung, lymph nodes, or pools of tissues from cases suspected of PRRSV, swine abortions, or respiratory diseases. These cells are plated till monolayers are confluent in approximately seventy-two hours, samples are inoculated, and the cell line is checked for the presence of virus by a fluorescent antibody test using SDOW 17 FITC conjugated antibody. The propagated virus, as produced in Example 12, is used to coat ELISA plates and the standard procedures for development of ELISA technology for detection of PRRSV antibodies have been described using the procedures of Witte et. al., Development of a Recombinant Nucleoprotein-Based Enzyme-Linked Immunosorbent Assay for Quantification of Antibodies against Porcine Reproductive and Respiratory Syndrome Virus, 7 Clinical and Diagnostic Laboratory Immunology, 700-702, (2000), the content and teachings of which are hereby incorporated by reference. Currently the ELISA test is considered as the gold-standard for monitoring the swine PRRSV antibodies.

[0129] Results:

[0130] The wild type PRRS virus can be detected in vitro by virus isolation. Additionally, the presence and quantity of PRRS antibodies can be detected using these immunodiagnostic assays. Other assays which would provide in vitro diagnostic tests for detecting wild type PRRS virus and antibodies and verifying PRRS diagnoses in swine herds include indirect fluorescent antibody tests and indirect immunoperoxidase tests. Such tests are well known in the art and could be developed using no more than ordinary skill.

EXAMPLE 14

[0131] This example shows the application of immunodiagnostic tools, (e.g. quantitative ELISA) for CD 151 which can be used to monitor swine fluid samples including platelet lysates, sperm lysates and swine alveolar macrophage lysates.

[0132] Materials and Methods:

[0133] Protein is detected quantitatively using the methods of Witte et. al., 2000. For example, the level of CD 151 in swine samples can be detected using these methods. Samples will be freeze-thawed. The level of protein will be monitored.

[0134] Results:

[0135] This example permits the mass screening of swine samples using a quantitative CD 151 ELISA. Additionally, the amount of CD 151 protein per ml of swine sample or per gram of tissue will be detectible using these methods.

EXAMPLE 15

[0136] This example illustrates that CD 151 from sources other than simian sources can be used to render a previously non-susceptible cell line susceptible to PRRSV infection.

[0137] Materials and Methods:

[0138] A sample of cellular material containing CD 151 is obtained from a swine. The RNA is extracted from this sample as previously described and then the porcine CD 151 is isolated using RT-PCR. The isolated CD 151 is then deposited in an appropriate mammalian expression vector which can be used to render previously non-susceptible cell lines susceptible to PRRSV infection. Examples of such cell lines include BHK-21. Additionally, by depositing the vector into previously susceptible cell lines, these cell lines can be used to overexpress the CD 151.

[0139] Results:

[0140] Previously non-susceptible cell lines are rendered susceptible to PRRSV infection after depositing a vector containing porcine CD 151 into the cell line. Previously susceptible cell lines can overexpress the inserted CD 151. Thus, CD 151 from any source can be used to transform cell lines including non-simian cell lines so that they express CD 151. This proves that, the source of the CD 151 (simian, porcine, etc.) is not relevant to practice the invention and that all aspects of the invention using simian CD 151 can also be accomplished using porcine or other similar CD 151 sequences.

EXAMPLE 16

[0141] This example proves that tetraspan CD 151 or its related homologues in other species such as equine CD 151 can be used to propagate the Arteriviruses from equine and other species.

[0142] Materials and Methods:

[0143] A heterologous CD 151 sequence is isolated and used to make recombinant cell lines as previously described. This cell line is then used to isolate and propagate the virus as previously described.

[0144] Results:

[0145] Similar to PRRSV, other Arteriviruses can be isolated and propagated to high titers in homologous and heterologous cell lines including non-simian cell lines. Thus, other Arteriviruses can be approached in the same manner as PRRSV in identifying methods of producing high titer vaccines in cell lines which were previously resistant to infection by the Arteriviruses and increasing virus production in cell lines which were previously susceptible to the Arteriviruses.

EXAMPLE 17

[0146] This example determined the DNA sequence and genomic organization of porcine CD 151.

[0147] Materials and Methods:

[0148] In order to determine the entire sequence of porcine CD 151, primers were designed in the end of each exon to the beginning of the next exon to determine the sequence of each intron. The primer pairs are shown below in Table 1. Inter- SEQ genic ID Region Primer Pair Sequence Direction No 1 5′-AGCCTCCTCAGGAATTCTGTC-3′ Forward 2 5′-GAAGCAGCAGTTGAAGGTGA-3′ Reverse 3 2 5′-TTTCACCTTCAACTGCTGCTTC-3′ Forward 4 5′-GCTGATGTAGTCGCTCTTG-3′ Reverse 5 3 5′-GCCACAGCCTACATCCTAGTG-3′ Forward 6 5′-AGTAGACGTAGGCCAGGACTC-3′ Reverse 7 4 5′-TCCTGCTGCTGCTCATCTTTC-3′ Forward 8 5′-CTCAGAGTGTCCTCCAGGTTCG-3′ Reverse 9 5 5′-TCAAGGCGAACCTGAAGGAC-3′ Forward 10 5′-TGTAGATGTTGGAGGCGTGG-3′ Reverse 11 6 & 7 5′-CTGTGGCAGCAACAACTCC-3′ Forward 12 5′-CTCCAGCTTCAGGCTCTTGT-3′ Reverse 13

[0149] The genomic DNA was extracted from the porcine alveolar macrophages (PAM cells) using a genomic DNA extraction kit and following the manufacturer's instructions (Dneasy Tissue Kit catalog # 69504, Qiagen, Valencia, Calif.). The PCR was set up as follows: Genomic DNA 200 ηg, 10×PCR buffer, 2 mM MgCl₂, DMSO 2.5 μl, 10 nmol of each dNTP, and 20 pmol of each primer. After initial denaturation at 95° C. for 5 minutes, 2.5 units Taq polymerase (Perkin Elmer, Foster City, Calif.) was added to the PCR mixture followed by 35 cycles at 95° C. for 30 seconds, annealing temperature specific for each intergenic region for 15 seconds, extension temperature of 72° C. for 1 minute, with the final extension at 72° C. for 45 minutes. The annealing temperatures for each intergenic region were as follows: intergenic region 1—57° C.; intergenic region 2—58° C.; intergenic region 3—59° C.; intergenic region 4—55° C.; intergenic region 5—53° C.; and intergenic regions 6 & 7—57° C. The PCR products were electrophoresed onto 1% agarose gel and the PCR band was excised and cloned to pGEM-T easy vector (Promega, Madison, Wis.). The sequence was then sequenced manually using a SequiTherm EXCEL II sequencing kit (Epicentre Technologies, catalog # SEM79100, Madison, Wis.) and following the manufacturer's instructions.

[0150] Results:

[0151] The sequence of porcine CD 151 is provided as SEQ ID No. 14. The intron sequence is known to vary between species as determined by sequence analysis of the human, rat, and mouse homologues of CD 151 and this is now also know to be true for porcine CD 151 which has shown little to no homology between the introns of porcine CD 151 and the introns of other animals which have CD 151.

[0152] The genomic organization of porcine CD 151 is presented in Table 2. The introns and exons are also provided with specific SEQ ID Nos as follows: SEQ ID No 15 is Exon 1; SEQ ID No 16 is Intron 1; SEQ ID No 17 is Exon 2; SEQ ID No 18 is Intron 2; SEQ ID No 19 is Exon 3; SEQ ID No 20 is Exon 4; SEQ ID No 21 is Intron 4; SEQ ID No 22 is Exon 5; SEQ ID No 23 is Intron 5; SEQ ID No 24 is Exon 6; SEQ ID No 25 is Intron 6; SEQ ID No 26 is Exon 7; SEQ ID No 27 is Intron 7; SEQ ID No 28 is Exon 8; and SEQ ID No 29 is Intron 8. All of the introns except for intron 3 are identified below and the sequence of intron 3 would be determined using methods similar to those used to obtain the remaining intron sequences. Of course, it is possible that there is no intron 3 sequence. However, if Intron 3 exists, it can obtained using porcine genomic DNA. TABLE 2 Exon 1 CGCCGCCACTGCCGGCCTCGGACGCGTGGACGAGCCTCCT SEQ ID No 15 CAGGAATTCTGTCCACCTGTCTCAGAGAGGAGCGGTCCCC AGCAGCCAG Intron 1 gtgagtgctgggcggggccgggtgaaagtccaccttggggcggtactgtctgaaagcgtggc SEQ ID No 16 cccaggt gctgagcggggcctgggccgcactgccccctgtccctcagggtggacaccccaggac agagcgagcggggcacctctggggtgtccctggggaggagcagagcccgcggcggt gtttctccctggggttggtgtggctgtcctcaccggtaatgaggaccagcacgggaagg ccccccaggcctgccacccgcccgccctggggtgggggggaaggaaggcaggcct gcccttgaacggaagcctgaggggcctcccggaggcccaggactaggctcgagagg gcagcacagcctgtctgtgagtggccttctccccctcccctccagcagccgctaggttcc tgccagcctgtgacgtggggcccggggaatgcttggggtggggtggggaagccttgc atagctcaccccgaaggtgcctgctggggcttcctaccctggctgccggcagggtgagt cagcgggtgacggctgggggtcctccacgcccccctcacggcccggggctctgggca gagaagctggcctgggggcagtgggccctccctcccttactggtactggggatggggg ctcctgagctgcgctcccaggaagtgtcccccttcccacggacactcccagagccttca ccagccaactgggactggtctggatgtctgtgtcccctccttctgtccccactggcatccc ccaggccggccctcccctgttccctgccccag Exon 2 CCCAGGATGGGCGAATTCGGCGAGAAGGGCGCGCCA SEQ ID No 17 TGCGGCCACCGTTTGCCTCAAGTACCTGCTTTTCACC TTCAACTGCTGCTTCTGG Intron 2 gtgaggagtgggcccccgcttcccgagcccggggctcagcccgtctctcacacccgg SEQ ID No 18 gccagacgtggtgattggtgtgcactgcccgcag Exon 3 CTGGCTGGCCTGGCCGTCATGGCAGTGGGCATCTGG SEQ ID No 19 ACGCTGGCCCTCAAGAGCGACTACATCAGCCTCCTG GCCTCGGGCACCTACCTGGCCACAGCCTACATCCTA GTGGTGGCGGGCATTGTTGTCATGGTGACCGGTGTTC TGGGCTGCTGTGCCACCTTCAAGGAGCGGAGGAACC TGCTGCGGCTG Exon 4 TACTTCATCCTGCTGCTGCTCATCTTTCTGCTGGAGA SEQ ID No 20 TCATCGCCGGAGTCCTGGCCTACGTCTACTACCAGCA G Intron 4 gtgcgcggctggggcgggccgcaggggcgcgtacacgcacagggtgtgcacgcgc SEQ ID No 21 atgagcacggacacgcacgtgccctgggaaggaagagatgcacacaggcagggaca cgtgcacgcgaccccacaggttccatgctgaccgtcgtgtcgtcaggccctggaggtg ggaccgtgtcaccagggaggacccccacaggggtggccagtctgcctgcagcaccca accacccacctgggggccccagtgtgccctccctgcccccgaccccccaccccatgcc atctgggtgacgttcccgggcacctgacccaccccaggcagcgtctgtctccagacctg tttggcaccttctgcgcctctcccgtctgtgcccatccccgcgctgccctcctccccgcttc ttagtctttgtggctgaagctgtcgccacctcgccacag Exon 5 CTGAGTGCAGAGCTCAAGGCGAACCTGAAGGACACT SEQ ID No 22 CTGAGCAAGCGCTACCGCCAGCCGGGCCACGAGGGT GTGACCAGCGCCACGGATAAGCTGCAGCAGGAG Intron 5 gtcggtgggtggcgccgggcggcgtctcccctgacgtctgtcggagccctggctgctg SEQ ID No 23 cgggggttgtggggaggggacggggctcagcccgggccatgttcccgtgcag Exon 6 TTCCACTGCTGTGGCAGCAACAACTCCCAGGACTGG SEQ ID No 24 CGGGACAGTGAGTGGATCCTCTCGGGTGAGGCAGGC GACCGTGTGGTTCCTGACAGCTGCTGCAAGACGGTG GTGGCGGGCTGCGGGCGGCGGGACCACGCCTCCAAC ATCTACAAAGTGGAG Intron 6 gtaggccagtgggggctgcacccgggatgctggaggcgggtgtccccgcacccgag SEQ ID No 25 gggcccggggctggggaagaggccccccctgccctcgacgcgccgctcacccccac tcccaccccag Exon 7 GGCGGCTGCATCACCAGGCTGGAGACCTTCATCCGG SEQ ID No 26 GAGCACCTGAGGATCATCGGGGCTGTGGGCATCGGC ATCGCCTGTGTGCAG Intron 7 tgcgggcgcggggcggcgcgggcgcggggcacggggcggcatgggcacaggcgc SEQ ID No 27 gtgctcatgccggctcttggctcag Exon 8 GTGTTCGGCATGATCTTCACGTGCTGCCTGTACAAGA SEQ ID No 28 GCCTGAAGCTGGAGCACTACTGA Intron 8 ctgcccacggacctgggcccacgcctgcaccgcagcttctcaggatgcgctgactact SEQ ID No 29 gacggctaggggctgcggtcccaggacgcggctcctcccctcccacactgccaggga ggtggtgtcctcatgccagggcccacgaccgtgccatcaccgcgactcctggggaccg ccaaccccagagggagcttcaagtgcctttcgctgccaccaaagtcccacggcccagc ccggtccctcctgcctctggggtggctggggcttgagctcaaaccgtaaaggccccatg cccgctgccctctcctttggggtattgttccctgataacctggctccgtcacggggctggt ctgtgccgagttaggcggaagctggccagcccggggccagtgccaggcggcaggca gcaggtgaggaagccgggtgcctgcctgctccaggaagagcaagagccctcccggc ctggcctctgcgcccacttacctgctgctcccaccaccatctaaaggcccaggtggacg gccacatgctgacgcccctccggggcagggcagccctctgggcctccttcactgctgta tccccatgcctaggactgctcctgctttgtgataggtgctcaataaacgcctgtggaccag aaaaaaaaaaaaaaaa

[0153] The discovered porcine CD 151 sequence was randomly matched with partial porcine CD 151 clones from deposited EST sequences in Genbank (Accession numbers: clone 1—BE233265; clone 2—AW314209; clone 3—AW786379) and compared with the published genomic sequence of human CD 151. Until the present invention, these previously published random CD 151 partial sequences were used only for expression studies and therefore, the full-length porcine CD 151 sequence had heretofore never been determined. Furthermore, these random partial EST sequences were not asociated with any known protein, gene, or function. It is also important to note that the use of the deposited EST sequences would not inherently lead one to the entire sequence of CD 151. This is especially true in light of the fact that the intron sequences of porcine CD 151 had no matches. Thus, this is the first report of the complete porcine mRNA and genomic sequences.

[0154]FIG. 10 is a schematic illustration of the porcine CD 151 sequence. The numbers 1-8 at the top of this figure represent the position of the CD 151 exons. Exons are also represented by the vertical rectangles in this figure which have horizontal bars within the rectangle. The introns are represented by the thin line connecting each of the exons. The rectangles having diagonal lines represent untranslated sequences. The start codon is represented by ATG and the stop codon is represented by TGA. The entire sequence ends with a poly-A tail.

EXAMPLE 18

[0155] This example identified single nucleotide polymorphisms (SNPs) of CD 151.

[0156] Materials and Methods:

[0157] Each of the introns will be analyzed by PCR cloning to determine the differences in SNPs and to correlate these SNPs with the susceptibility of cells to PRRSV infection. The sequence data from each of the introns from the PAM cells is obtained as described in Example 17 and the primers are designed to amplify just the each of the introns and then are used to amplify the each of the corresponding introns in the various susceptible and non-susceptible cell lines. The data obtained will then be analyzed using the GCG program (University of Wisconsin, Madison, Wis.).

[0158] Results:

[0159] The single nucleotide polymorphism in the introns and exons of any gene may play important roles in gene expression. The sum of the sequence variation of the introns may also play an important role in the expression of the gene in the cell thereby leading to variations in susceptibility to PRRSV infection.

EXAMPLE 19

[0160] This example determines the chromosomal localization of porcine CD 151.

[0161] Materials and Methods:

[0162] Chromosomal localization is performed by Flourescent In-Situ Hybridization (FISH). The chromosome spreads are prepared by standard methods. The leukocytes will be collected from heparinized blood, the red blood cells (RBC's) are lysed and the chromosome is spread on the slides. The slides are denatured in 70% formamide in 2×SSC at 70° C. The slides are then incubated with biotin labeled probe (genomic CD 151). The post-hybridization washes will be performed by standard methods and the binding detected by standard methods using flourescein labeled avidin as described by Roland M. Nadore in Flourescence In-Situ Hybridization Using Whole Chromosome Library Probes, Methods In Molecular Biology; edited by Lorette Javis (pages 371-377), the teachings of which are hereby incorporated by reference (Nadore, Roland M. 1999 Immunocytochemical Methods and Protocols (2^(nd) ed.), Methods in Molecular Biology, pages 371-377).

[0163] Results:

[0164] In addition to identifying the chromosomal localization of the porcine CD 151, this example also helps to localize the other diseases associated with this chromosome. This would provide a distinct advance over the prior art in that the CD 151 gene may be linked to other disease resistance genes or production traits, which effect the breeding status, such as meat carcass quality traits. Gene location will help predict the collateral effects of selection for CD 151. Once other diseases associated with this chromosome have been correlated with CD 151, strategies for breeding can be developed. Of course, it would be most desirable to be able to select for PRRSV resistance and still maintain carcass quality.

EXAMPLE 20

[0165] This example provides a transcriptional profile of the porcine CD 151 gene.

[0166] Materials and Methods:

[0167] Various susceptible and nonsusceptible tissues were collected from pigs and the tissue was ground such that the RNA could be extracted using the acid guanidinium and phenol chloroform method as described by Chomczynski and Sacchi, Single-step method of RNA isolation by Acid Quadnidinium thiocyanate-phenol-choloroform extraction. 62 Anal. Biochem., 156-159.(1987), the teachings of which are hereby incorporated by reference. The total RNA was run on 1% formaldehyde agarose gel and transferred to the nylon membrane. The CD 151 transcripts was then detected by Northern Blotting using radiolabeled CD 151 mRNA probe following standard protocols. Equal amounts of RNA were loaded into each well. The sizes of the transcripts were compared by using the known radiolabeled RNA markers. The transcript amount was quantified using the GAPDH mRNA probe as the control. After post-hybridization washes and autoradiographs, the results were recorded.

[0168] Results:

[0169] This example identified two transcripts of CD 151. The size of these transcripts is not specifically known. However, the first transcript is larger/upper and the second transcript is lower/smaller In the first experiment, both the upper and lower transcripts were present in susceptible tissues (spleen, lung, kidney and heart). However, nonsusceptible tissues (muscle and liver) had only the upper transcript. Thus, the larger (upper) transcript alone is indicative of PRRSV susceptibility whereas the smaller (lower) transcript alone is present in nonsusceptible tissues.

EXAMPLE 21

[0170] This example demonstrates the RNA-binding activity of porcine CD 151.

[0171] Materials and Methods:

[0172] Porcine tissue (100 mg) was frozen in liquid nitrogen and ground in a micro-dismembranator for 30 seconds. The tissue pellet was resuspended in 100 μl of 0.01M phosphate buffered saline (PBS) and 900 μl of RIPA lysis buffer (10 mM TrisHCl pH 8.0, 0.14 M NaCl₂, 1% Triton X-100, 1% Sodium Deoxycholate, 0.1% SDS, and 0.2/mL of Aprotinin), vortexed and incubated at 37° C. for 30 minutes. The tissue sample was then centrifuged at 8,000 rpm for 10 minutes to remove the debris. The supernatant was collected and used for immunoprecipitation with anti-CD 151 monoclonal antibody (PharMingen, San Diego, Calif., Catalog No. 556056) Followed by northwestern assay using radiolabeled PRRSV 3′ UTR RNA, as described above.

[0173] Results:

[0174] Porcine CD 151 has RNA binding activity as shown in the northwestern blot of FIG. 11. This blot is from muscle and clearly demonstrates the RNA binding activity of porcine CD 151. This verifies that porcine CD 151 functions similarly to simian CD 151 and is responsible for RNA entry and is therefore the susceptibility factor for PRRSV.

[0175] The correct size and also the amount of each transcript will be analyzed and correlated with disease susceptibility of each tissue to PRRSV.

EXAMPLE 22

[0176] This example determines the cytopathology and viral titers in non-simian cell lines transfected with porcine CD 151.

[0177] Materials and Methods:

[0178] BHK-21 cells were stably transfected with porcine CD 151 as described in Example 1. The construct of porcine CD 151 used for this experiment lacked nine amino acids of the open reading frame. This clone was transfected in BHK-21 and selected for with G-418 for stable transfectants. This clone was then tested for PRRSV susceptibility. The PRRSV titers were then tested by titration experiments. The PRRSV was infected in serial dilutions (1:10, then 10-fold dilutions further down) for one hour at 37° C. The monolayer was then washed in PBS and then replaced with 1 ml of MEM. The 100 μl of supernatant was collected at 0, 24, 36, 48, and 72 hours post-infection. After 72 hours, the cells were stained for PRRSV by direct fluorescent antibody test (FA) using SDOW-17 nucleoprotein mAB. The virus collected at different time intervals was titrated in the MARC cells.

[0179] Results:

[0180] As expected, no cytopathic effects were observed in BHK-21 cells. However, the stable transfection of MARC cells with CD 151 did lead to enhanced PRRSV production. This provides further verification that the porcine CD 151 functions similarly to the other previously identified CD 151 sequences. However, the construct without the first nine amino acids did not function quite as well. Thus, porcine CD 151 can be similarly used to produce PRRSV in non-simian cell lines.

EXAMPLE 23

[0181] This example determined and compared the amount of CD 151 expressed in different tissues.

[0182] Methods and Materials:

[0183] Various susceptible and non-susceptible tissues were collected from pigs and the tissue was ground such that the RNA could be extracted using the acid guanidinium and phenol chloroform method as described by Chomczynski and Sacchi. The total RNA was then run on 1% formaldehyde agarose gel and transferred to the nylon membrane. The CD 151 transcripts were detected by Northern blotting using radiolabeled CD 151 mRNA as the probe and following standard protocols. An equal amount of RNA was loaded into each well and then the known radiolabeled RNA markers were used to compare the sizes of the transcripts. The transcript amount was quantified using the GAPDH mRNA probe as the control. The results were recorded after post hybridization washes and autoradiographs.

[0184] Results:

[0185] Northern blot assays of porcine tissues for CD 151 mRNAs of any gene will indicate the amount of protein expressed in the tissue. The presence of the correct size and the amount of the transcript are very important in determining protein expression in the tissue. Two transcripts were observed as discussed previously. Each tissue has its own transcriptional profile for CD151.

EXAMPLE 24

[0186] This example compares the transcriptional profiles of tissues as shown by Example 20 and compares the results for different breeds of pigs.

[0187] Methods and Materials:

[0188] Transcriptional profiles are prepared as described in Example 20. However, differences in these profiles are correlated with various susceptible and non-susceptible breeds of pigs.

[0189] Results:

[0190] The amount of each transcript in different tissues from different breeds of pigs will be correlated with the relative PPRRSV susceptibility of each breed. Nonsusceptible breeds or breeds with reduced susceptibility to PRRSV infection will show decreased levels of CD 151 in the tissues when compared with levels from these same tissues but from other sources. The transcriptional profile of individual pigs in different breeds of swine will be used to develop selection criteria for improved swine breeding.

EXAMPLE 25

[0191] This example determines the tissue distribution of porcine CD 151.

[0192] Methods and Materials:

[0193] Different porcine tissues were collected an 100 mg of the tissue was frozen in liquid nitrogen and ground using a microdismembrator with a pulse of 30 seconds. The ground tissues was resuspended in 1 ml of RIPA buffer. The sample was then incubated at room temperature for 30 minutes in the shaker. The protein sample was then centrifuged at 6,000 rpm for 5 minutes. The supernatant was then electrophorosed to a 10% SDS-PAGE gel. Next, the proteins were transferred to the nitrocellulose membrane blocked in 10% horse serum and the CD 151 antibody was added 1:500 in blocking solution. The membrane was then washed three times for 15 minutes before incubating in secondary anti-mouse HRPO conjugate (Vector Laboratories, Burlingame, Calif.) (1:10,000). The membranes were then developed in membrane TMB conjugate (Kirkegaard & Perry Laboratories, Inc., Gaithersburg, Md.).

[0194] In order to determine the genomic organization of porcine CD 151, an anti-CD 151 monoclonal antibody 14A2.H1 (Pharmingen, San Diego, Calif.) raised against human CD 151 was used. A western blot assay was then performed and the results analyzed for CD 151 expression levels. The amount of two isoforms of porcine CD 151 will be quantified and correlated with PRRSV susceptibility. These parameters will also be used to aid in the selection of swine for breeding. Ultimately, the criteria could be assigned different weights for breeding and selection.

[0195] Results:

[0196] It was shown that pig muscle and heart tissue have large amounts of CD 151 as two bands were identified using the western blot assay. One band was approximately 60 kDA and the other band was approximately 30 kDA. Because the expression of the CD 151 gene within a cell is determined by the genomic organization of the gene, the expression of CD 151 in high quantities or in low quantities is directly related to this organization. The organization also indicates whether there are other factors such as enhancers or inhibitors of gene expression leading to the different susceptibility of pigs to PRRS disease.

EXAMPLE 26

[0197] This example illustrates the critical role of the YRSL domain which is present at the carboxy end of CD 151 in the biology of PRRSV.

[0198] Materials and Methods

[0199] To study the effect of mutations of the cytoplasmic tails of CD 151 on PRRSV RNA entry, the effects of these mutations will be checked by their effects on PRRSV infectivity. The presence of the virus will be checked by immunofluorescence assay. Briefly, PCR-based mutogenesis will be performed on two constructs of CD 151 (simian and porcine) to study the effect of these mutations on PRRSV infectivity.

[0200] Results:

[0201] The CD 151 molecule contains a YRSL (SEQ ID No 29) sequence at the cytoplasmic tail. It is believed that this sequence is in the YXXL (SEQ ID No 36) motif or domain. This motif and especially the YRSL sequence is a known RNA binding domain located at the carboxy terminal. In such a domain, the XX residues may be mutated without any change in internalization. The L residue is a critical hydrophobic residue. If the cytoplasmic tail of CD 151 plays a critical role in PRRSV RNA entry, the mutated CD 151 will be unable to restore the PRRSV infectivity in the BHK-21 cell line. It is believed that this will be the case if the Y or L are mutated. However, if the R or S are mutated, it is believed that there will be no effect on the RNA binding ability of the cytoplasmic tail. Accordingly, such mutated CD 151 sequences would be able to restore PRRSV infectivity in the BHK-21 cell line. In such situations, it is believed that the YRSL sequence acts as one of the signals at the carboxy terminal of CD 151. This would correlate with other known things that enter cells at the end of the endocytic cycle which have signals at their carboxy terminals. Endocytosis includes the formation of clathrin coated pits that bud from the cytoplasmic membrane into the cell. PRRSV enters through clathrin coated pits. It is known that CD 151 is localized in endosomes of target organs such as endothelial cells and may participate in the entry of PRRSV through endosomes. PRRS has many genotypes and over 75 immunotypes but all isolates use a common entry pathway. Accordingly, the information developed from this example would be used to find out if any lines of pigs have mutations in this critical sequence of CD 151.

[0202] Discussion

[0203] Viruses are obligatory internal parasites that have limited genetic material for replication. Viruses often utilize host cellular factors, in the form of RNA binding proteins, transcription factors, proteases, and membrane factors for their replication. RNA binding proteins could play roles in transcription, translation, orientation, and transport of viral RNA. To understand how viral RNA replication proceeds, it is important to identify and characterize these proteins. There is no report of identification of host cellular proteins binding to the 3′ UTR of PRRSV.

[0204] Here the identification of a novel 29 kD glycoprotein, simian CD 151, which binds to the 3′UTR of PRRSV is reported. CD 151 is a transmembrane glycoprotein, belonging to the tetraspan or transmembrane 4 superfamily of cellular proteins. Tetraspans have four highly conserved hydrophobic domains spanning the lipid bilayer and two extracellular domains. The N and C terminals are found in the cytoplasm. The simian CD 151 shares 98% homology with PETA-3, which is found mainly in endothelial cell membranes, platelets and megakaryocytes, epithelium, lung, muscle, Schwann cells, and glomeruli. This protein has been shown to be upregulated in human T cells transformed by T cell leukemia virus type I and has been named SFA-1. Significant amounts of PETA-3 are present in intracellular compartments, localized to perinuclear vesicles, accounting for 66% of the total amount of PETA-3 protein present in endothelial cells. Tetraspan CD 151 is required for the early step in metastasis of tumors and is involved in interactions with the integrins in hemopoietic cell lines, modulation of cell-cell adhesions, and transmembrane signaling through protein-protein interactions.

[0205] After demonstrating that CD 151 binds to the 3 ′UTR of PRRSV, the correlation between the presence of CD 151 and susceptibility to PRRSV infection was tested. It was found that MA 104, MARC, COS-7 and Vero cell lines which are all derived from kidney cells have CD 151. However, BHK-21 and MDBK cells are also derived from kidney cells, but they lack CD 151. Thus, CD 151 as a kidney specific protein is ruled out. The PRRSV does not enter BHK-21 cells, but the transfection of these cells with either the PRRSV RNA or the infectious cDNA clone results in productive viral infection without spreading to neighboring cells. Thus, it was reasoned that although BHK-21 cells support the replication of PRRSV RNA, they lack the cellular factors required for the entry of the virus or viral RNA. Since it was found that CD 151 is a transmembrane protein, it was reasoned that it might have a role in entry of PRRSV and/or viral RNA. There is a previous report that CD 9, another tetraspan, renders MDBK a non-susceptible cell line, susceptible to canine distemper virus infection and functions as an entry molecule. To prove that CD 151 is one of the susceptibility factors of PRRSV infection, it was determined that BHK-21 cells expressing CD 151 get infected by PRRSV while the parent cell line lacking CD 151 did not get infected. Thus, because CD 151 is a transmembrane molecule, it might play a role in virus entry or viral RNA entry into BHK-21 cells.

[0206] Entry of the virus into cells occurs by the interaction of viral proteins with specific viral receptors present on the cell membrane. These receptors are very important determinants of susceptibility to viral infection. Previous studies have demonstrated that PRRSV binds to a heparin-like molecule, and entry of the virus occurs by receptor-mediated endocytosis. Low pH in these vesicles is essential for the productive infection. Coimmunoprecipitation was performed to determine if there is any interaction between PRRSV proteins and CD 151, however, there was no evidence for direct protein-protein interaction between them. This is in agreement to the previous observation that CD 9, another tetraspan is a susceptibility factor for canine distemper but it does not directly interact with the viral proteins. For a protein to be a receptor, it has to interact with the viral proteins; thus, the CD 151 does not function as the receptor. Because CD 151 is present in the vesicles and also in the membranes, its role as an RNA transporter molecule is predicted based on two observations: first, it rendered non-susceptible BHK-21 cells susceptible to viral infection and secondly, MARC cells that overexpress CD 151 (by stable transfection) exhibit a 100-fold increase in virus production as compared to the native cell line. This effect of CD 151 on viral replication may be explained by increased cellular uptake of the viral RNA during the entry of the virus with CD 151 functioning as an RNA-transport molecule. This process is shown schematically in FIG. 9. There are previous data where the RNA binding proteins are predicted to function as RNA transporter molecules. Testis/brain RNA binding protein interacts with the 3′UTR of the mRNA and it transports mRNA to specific intracellular sites where they are translated. This protein is also reported to transport the mRNAs between cells. In tobacco mosaic virus, a 30 kD movement protein is involved in transport of the viral RNA from cell to cell via the plasmodesmata. In beet necrotic yellow virus, proteins p 42, p 14, and p 13 are involved in the movement of viral RNA through the plasmodesmata by interaction with the viral RNA. There is no report of an RNA transport molecule in animal viruses. In PRRSV infection, the CD 151 either alone or in conjugation with other proteins might act as the RNA transporter molecule for entry into the cytoplasm after the virus uncoats in the vesicles. Thus, the present invention demonstrates that CD 151 is involved in the replication of PRRS virus mainly as a viral RNA entry molecule.

[0207] To determine whether the CD 151 transmembrane protein plays a role in entry of the virus/viral RNA into the cell, BHK-21 cells were chosen for testing because BHK-21 cells are resistant to PRRSV infection. However, when BHK-21 cells are transfected with either the viral RNA or the infectious cDNA clone of PRRSV, they support the replication of the virus. Thus the resistance factor in BHK-21 cells might be associated with the entry molecule. The fact that BHK-21 cells lack CD 151 was definitively shown by RT-PCR (FIG. 5, lane 6) using CD 151 specific primers. BHK-21 cells expressing CD 151 were obtained by stable transfection as described above in the Materials and Methods. These transfected cells were infected with PRRSV and tested for virus production by immunohistochemistry. Notably, it was found that the CD 151 transfected cells became infected with PRRSV but the parent BHK-21 cells lacking CD 151 (verified in FIG. 6) did not become infected.

[0208] Another advantageous aspect of the present invention is that the baby hamster kidney (BHK) cell line used in these experiments is not of simian origin. Thus it differs from all other cell lines used for propagating PRRSV which are of simian origin. This provides a great advantage because the use of non-simian cells lines poses no risk of transmission of primate or simian viruses to pigs, especially xenotransplanted pigs. By using non-simian cell lines to propagate PRRSV, primate and/or simian viruses will not be introduced into swine populations and will therefore not pose a risk to the human population. Also, because these cells expressing CD 151 have higher titers of PRRSV, they are more convenient and economically useful for propagating PRRSV for vaccine production. Advantageously, these cells can be used to make killed and live PRRS virus vaccines and serodiagnostic assays.

[0209] Finally, the present invention determined the DNA sequence and genomic organization of porcine CD 151. Such knowledge will aid in the development of a DNA-based PCR which could be done on ear-notched biopsies. If a live animal was not available, testing could also be done using germplasm, semen, and flushed ova. Such a design permits germplasm from deceased animals to be used several years and generations after death in order to improve the herd as a whole. If was further found that porcine CD 151 had PRRSV RNA-binding activity in swine tissues and that porcine CD 151 had only 84% sequence homology with known CD 151 sequences for humans, monkeys, and mice. Additionally, the present invention has enabled the determination of porcine CD 151 mRNA. Such a sequence can be determined by combining the exons of Table 2 in sequential order and allowing for the transcription from the DNA sequences of these exons into RNA. Such a sequence which can lead to mRNA sequence is provided herein as SEQ ID No. 38.

[0210] A monoclonal antibody designated 7G10 has been developed. this antibody completely blocks PRRSV infection in cell culture. This antibody was made against a host cell protein of the MARC cell line and is an IgA isotype expressing high neutralizing activity against PRRSV. On the basis of virus overlay protein blot assay (VOPA), 7G10 recognizes a receptor of PRRSV and is thus able to cause the neutralization of PRRSV. These specific characteristics make 7G10 applicable in the swine industry for preventing the transmission of PRRSV

1 38 1 1465 DNA Simian Gen. Sp. misc_feature (451)..(451) n is a, c, g or t 1 gtcccggact ccgacgagtg gtagccccag gatgggtgag tttaacgaga agaagacaac 60 atgtggcacc gtttgcctca agtacctgct gtttacctac aactgctgct tctggctggc 120 cggcctggct gtcatggcag tgggcatctg gacgctggcc ctcaagagtg actacatcag 180 cctcctggcc tcgggcacct acctggccac agcctacatc ctggtggtgg cgggcgctgt 240 cgtcatggtg accggggtct tgggctgctg tgccaccttc aaggagcgtc ggaacctgct 300 gcgcctgtac ttcatcctgc tcctcatcat ctttctgctg gagatcatcg ctggtgtcct 360 cgcctatgtc tactaccagc agctgaacac agagctcaag gagaacctta aggacaccat 420 ggccaagcgc taccaccagc cgggtcacga ngccgtgacc agcgctgtgg accaactgca 480 gcangagttc cactgctgtg gcagcaacaa ctcacaggac tggcgggaca gtgaagtgga 540 tccgcttaag ggaagnccgt ggccgcgtgg tccccgatag ctgcttgcaa gacggtggtg 600 gctggttgtg ggcaancggg accacgcctt caacatttac aaggnggang gnggnttcat 660 caccaagttg gagaccttca tccaggagca cctcagggtc attggggctg tggggactgg 720 cattgcctgt gtgcaggtct ttggcatgat cttcacatgc tgcctgtaca ggagcctcaa 780 gctggagcac tactgaccct gccctgggct tggccgcggc tctgtgcttt gctgctgctg 840 cacccaacta ctgagctgag accactgagt accaggggct gggntccctg atgacaccca 900 ccntgtgcca tcaccanaac tttggggacc ccaaccccag aggcaagctt caagtgcctt 960 tcgctgcaca ccaaagccca gcagggaagt gaggggggct ggcgggacga cggtatgggg 1020 gtgttttgtg gggctgcctg aacacattct gcctggtggt cagatgcagg ctagccgggg 1080 ccttgctgag tagggcaagg ccgagtgttc ccagcagggg gagaagccct tcacatccca 1140 ggcccttcag ggattagggc tttgccttgc agccacatgg ccccatccca gtntgagaag 1200 ctgagtaagc tctgaccctt gggcctgggc ctctgcccct ccccacccag gcctcgtctc 1260 cctcagagcc cctgctgtct tccccaccgc agtcaccacc acccgaaatg ccacatggtc 1320 acttgtgcac tgccccgtcc atgtgcctgt gtggggcagg ggcctcccgg ttttgttcac 1380 tgctgtaccc agatgcctac aaccatccct gccacataca ggtgctcaat aaacacttgt 1440 ggggcagatg gacgaaaaaa aaaaa 1465 2 21 DNA Simian Gen. Sp. 2 agcctcctca ggaattctgt c 21 3 20 DNA Simian Gen. Sp. 3 gaagcagcag ttgaaggtga 20 4 22 DNA Simian Gen. Sp. 4 tttcaccttc aactgctgct tc 22 5 19 DNA Simian Gen. Sp. 5 gctgatgtag tcgctcttg 19 6 21 DNA Simian Gen. Sp. 6 gccacagcct acatcctagt g 21 7 21 DNA Simian Gen. Sp. 7 agtagacgta ggccaggact c 21 8 21 DNA Simian Gen. Sp. 8 agtagacgta ggccaggact c 21 9 22 DNA Simian Gen. Sp. 9 ctcagagtgt cctccaggtt cg 22 10 20 DNA Simian Gen. Sp. 10 tcaaggcgaa cctgaaggac 20 11 20 DNA Simian Gen. Sp. 11 tgtagatgtt ggaggcgtgg 20 12 19 DNA Simian Gen. Sp. 12 ctgtggcagc aacaactcc 19 13 20 DNA Simian Gen. Sp. 13 ctccagcttc aggctcttgt 20 14 3161 DNA Simian Gen. Sp. 14 cgccgccact gccggcctcg gacgcgtgga cgagcctcct caggaattct gtccacctgt 60 ctcagagagg agcggtcccc agcagccagg tgagtgctgg gcggggccgg gtgaaagtcc 120 accttggggc ggtactgtct gaaagcgtgg ccccaggtgc tgagcggggc ctgggccgca 180 ctgccccctg tccctcaggg tggacacccc aggacagagc gagcggggca cctctggggt 240 gtccctgggg aggagcagag cccgcggcgg tgtttctccc tggggttggt gtggctgtcc 300 tcaccggtaa tgaggaccag cacgggaagg ccccccaggc ctgccacccg cccgccctgg 360 ggtggggggg aaggaaggca ggcctgccct tgaacggaag cctgaggggc ctcccggagg 420 cccaggacta ggctcgagag ggcagcacag cctgtctgtg agtggccttc tccccctccc 480 ctccagcagc cgctaggttc ctgccagcct gtgacgtggg gcccggggaa tgcttggggt 540 ggggtgggga agccttgcat agctcacccc gaaggtgcct gctggggctt cctaccctgg 600 ctgccggcag ggtgagtcag cgggtgacgg ctgggggtcc tccacgcccc cctcacggcc 660 cggggctctg ggcagagaag ctggcctggg ggcagtgggc cctccctccc ttactggtac 720 tggggatggg ggctcctgag ctgcgctccc aggaagtgtc ccccttccca cggacactcc 780 cagagccttc accagccaac tgggactggt ctggatgtct gtgtcccctc cttctgtccc 840 cactggcatc ccccaggccg gccctcccct gttccctgcc ccagccccag gatgggcgaa 900 ttcggcgaga agggcgcgcc atgcggccac cgtttgcctc aagtacctgc ttttcacctt 960 caactgctgc ttctgggtga ggagtgggcc cccgcttccc gagcccgggg ctcagcccgt 1020 ctctcacacc cgggccagac gtggtgattg gtgtgcactg cccgcagctg gctggcctgg 1080 ccgtcatggc agtgggcatc tggacgctgg ccctcaagag cgactacatc agcctcctgg 1140 cctcgggcac ctacctggcc acagcctaca tcctagtggt ggcgggcatt gttgtcatgg 1200 tgaccggtgt tctgggctgc tgtgccacct tcaaggagcg gaggaacctg ctgcggctgt 1260 acttcatcct gctgctgctc atctttctgc tggagatcat cgccggagtc ctggcctacg 1320 tctactacca gcaggtgcgc ggctggggcg ggccgcaggg gcgcgtacac gcacagggtg 1380 tgcacgcgca tgagcacgga cacgcacgtg ccctgggaag gaagagatgc acacaggcag 1440 ggacacgtgc acgcgacccc acaggttcca tgctgaccgt cgtgtcgtca ggccctggag 1500 gtgggaccgt gtcaccaggg aggaccccca caggggtggc cagtctgcct gcagcaccca 1560 accacccacc tgggggcccc agtgtgccct ccctgccccc gaccccccac cccatgccat 1620 ctgggtgacg ttcccgggca cctgacccac cccaggcagc gtctgtctcc agacctgttt 1680 ggcaccttct gcgcctctcc cgtctgtgcc catccccgcg ctgccctcct ccccgcttct 1740 tagtctttgt ggctgaagct gtcgccacct cgccacagct gagtgcagag ctcaaggcga 1800 acctgaagga cactctgagc aagcgctacc gccagccggg ccacgagggt gtgaccagcg 1860 ccacggataa gctgcagcag gaggtcggtg ggtggcgccg ggcggcgtct cccctgacgt 1920 ctgtcggagc cctggctgct gcgggggttg tggggagggg acggggctca gcccgggcca 1980 tgttcccgtg cagttccact gctgtggcag caacaactcc caggactggc gggacagtga 2040 gtggatcctc tcgggtgagg caggcgaccg tgtggttcct gacagctgct gcaagacggt 2100 ggtggcgggc tgcgggcggc gggaccacgc ctccaacatc tacaaagtgg aggtaggcca 2160 gtgggggctg cacccgggat gctggaggcg ggtgtccccg cacccgaggg gcccggggct 2220 ggggaagagg ccccccctgc cctcgacgcg ccgctcaccc ccactcccac cccagggcgg 2280 ctgcatcacc aggctggaga ccttcatccg ggagcacctg aggatcatcg gggctgtggg 2340 catcggcatc gcctgtgtgc aggtgcgggc gcggggcggc gcgggcgcgg ggcacggggc 2400 ggcatgggca caggcgcgtg ctcatgccgg ctcttggctc aggtgttcgg catgatcttc 2460 acgtgctgcc tgtacaagag cctgaagctg gagcactact gacctgccca cggacctggg 2520 cccacgcctg caccgcagct tctcaggatg cgctgactac tgacggctag gggctgcggt 2580 cccaggacgc ggctcctccc ctcccacact gccagggagg tggtgtcctc atgccagggc 2640 ccacgaccgt gccatcaccg cgactcctgg ggaccgccaa ccccagaggg agcttcaagt 2700 gcctttcgct gccaccaaag tcccacggcc cagcccggtc cctcctgcct ctggggtggc 2760 tggggcttga gctcaaaccg taaaggcccc atgcccgctg ccctctcctt tggggtattg 2820 ttccctgata acctggctcc gtcacggggc tggtctgtgc cgagttaggc ggaagctggc 2880 cagcccgggg ccagtgccag gcggcaggca gcaggtgagg aagccgggtg cctgcctgct 2940 ccaggaagag caagagccct cccggcctgg cctctgcgcc cacttacctg ctgctcccac 3000 caccatctaa aggcccaggt ggacggccac atgctgacgc ccctccgggg cagggcagcc 3060 ctctgggcct ccttcactgc tgtatcccca tgcctaggac tgctcctgct ttgtgatagg 3120 tgctcaataa acgcctgtgg accagaaaaa aaaaaaaaaa a 3161 15 89 DNA Simian Gen. Sp. 15 cgccgccact gccggcctcg gacgcgtgga cgagcctcct caggaattct gtccacctgt 60 ctcagagagg agcggtcccc agcagccag 89 16 795 DNA Simian Gen. Sp. 16 gtgagtgctg ggcggggccg ggtgaaagtc caccttgggg cggtactgtc tgaaagcgtg 60 gccccaggtg ctgagcgggg cctgggccgc actgccccct gtccctcagg gtggacaccc 120 caggacagag cgagcggggc acctctgggg tgtccctggg gaggagcaga gcccgcggcg 180 gtgtttctcc ctggggttgg tgtggctgtc ctcaccggta atgaggacca gcacgggaag 240 gccccccagg cctgccaccc gcccgccctg gggtgggggg gaaggaaggc aggcctgccc 300 ttgaacggaa gcctgagggg cctcccggag gcccaggact aggctcgaga gggcagcaca 360 gcctgtctgt gagtggcctt ctccccctcc cctccagcag ccgctaggtt cctgccagcc 420 tgtgacgtgg ggcccgggga atgcttgggg tggggtgggg aagccttgca tagctcaccc 480 cgaaggtgcc tgctggggct tcctaccctg gctgccggca gggtgagtca gcgggtgacg 540 gctgggggtc ctccacgccc ccctcacggc ccggggctct gggcagagaa gctggcctgg 600 gggcagtggg ccctccctcc cttactggta ctggggatgg gggctcctga gctgcgctcc 660 caggaagtgt cccccttccc acggacactc ccagagcctt caccagccaa ctgggactgg 720 tctggatgtc tgtgtcccct ccttctgtcc ccactggcat cccccaggcc ggccctcccc 780 tgttccctgc cccag 795 17 92 DNA Simian Gen. Sp. 17 ccccaggatg ggcgaattcg gcgagaaggg cgcgccatgc ggccaccgtt tgcctcaagt 60 acctgctttt caccttcaac tgctgcttct gg 92 18 91 DNA Simian Gen. Sp. 18 gtgaggagtg ggcccccgct tcccgagccc ggggctcagc ccgtctctca cacccgggcc 60 agacgtggtg attggtgtgc actgcccgca g 91 19 192 DNA Simian Gen. Sp. 19 ctggctggcc tggccgtcat ggcagtgggc atctggacgc tggccctcaa gagcgactac 60 atcagcctcc tggcctcggg cacctacctg gccacagcct acatcctagt ggtggcgggc 120 attgttgtca tggtgaccgg tgttctgggc tgctgtgcca ccttcaagga gcggaggaac 180 ctgctgcggc tg 192 20 75 DNA Simian Gen. Sp. 20 tacttcatcc tgctgctgct catctttctg ctggagatca tcgccggagt cctggcctac 60 gtctactacc agcag 75 21 444 DNA Simian Gen. Sp. 21 gtgcgcggct ggggcgggcc gcaggggcgc gtacacgcac agggtgtgca cgcgcatgag 60 cacggacacg cacgtgccct gggaaggaag agatgcacac aggcagggac acgtgcacgc 120 gaccccacag gttccatgct gaccgtcgtg tcgtcaggcc ctggaggtgg gaccgtgtca 180 ccagggagga cccccacagg ggtggccagt ctgcctgcag cacccaacca cccacctggg 240 ggccccagtg tgccctccct gcccccgacc ccccacccca tgccatctgg gtgacgttcc 300 cgggcacctg acccacccca ggcagcgtct gtctccagac ctgtttggca ccttctgcgc 360 ctctcccgtc tgtgcccatc cccgcgctgc cctcctcccc gcttcttagt ctttgtggct 420 gaagctgtcg ccacctcgcc acag 444 22 105 DNA Simian Gen. Sp. 22 ctgagtgcag agctcaaggc gaacctgaag gacactctga gcaagcgcta ccgccagccg 60 ggccacgagg gtgtgaccag cgccacggat aagctgcagc aggag 105 23 110 DNA Simian Gen. Sp. 23 gtcggtgggt ggcgccgggc ggcgtctccc ctgacgtctg tcggagccct ggctgctgcg 60 ggggttgtgg ggaggggacg gggctcagcc cgggccatgt tcccgtgcag 110 24 159 DNA Simian Gen. Sp. 24 ttccactgct gtggcagcaa caactcccag gactggcggg acagtgagtg gatcctctcg 60 ggtgaggcag gcgaccgtgt ggttcctgac agctgctgca agacggtggt ggcgggctgc 120 gggcggcggg accacgcctc caacatctac aaagtggag 159 25 123 DNA Simian Gen. Sp. 25 gtaggccagt gggggctgca cccgggatgc tggaggcggg tgtccccgca cccgaggggc 60 ccggggctgg ggaagaggcc ccccctgccc tcgacgcgcc gctcaccccc actcccaccc 120 cag 123 26 87 DNA Simian Gen. Sp. 26 ggcggctgca tcaccaggct ggagaccttc atccgggagc acctgaggat catcggggct 60 gtgggcatcg gcatcgcctg tgtgcag 87 27 80 DNA Simian Gen. Sp. 27 gtgcgggcgc ggggcggcgc gggcgcgggg cacggggcgg catgggcaca ggcgcgtgct 60 catgccggct cttggctcag 80 28 60 DNA Simian Gen. Sp. 28 gtgttcggca tgatcttcac gtgctgcctg tacaagagcc tgaagctgga gcactactga 60 29 659 DNA Simian Gen. Sp. 29 cctgcccacg gacctgggcc cacgcctgca ccgcagcttc tcaggatgcg ctgactactg 60 acggctaggg gctgcggtcc caggacgcgg ctcctcccct cccacactgc cagggaggtg 120 gtgtcctcat gccagggccc acgaccgtgc catcaccgcg actcctgggg accgccaacc 180 ccagagggag cttcaagtgc ctttcgctgc caccaaagtc ccacggccca gcccggtccc 240 tcctgcctct ggggtggctg gggcttgagc tcaaaccgta aaggccccat gcccgctgcc 300 ctctcctttg gggtattgtt ccctgataac ctggctccgt cacggggctg gtctgtgccg 360 agttaggcgg aagctggcca gcccggggcc agtgccaggc ggcaggcagc aggtgaggaa 420 gccgggtgcc tgcctgctcc aggaagagca agagccctcc cggcctggcc tctgcgccca 480 cttacctgct gctcccacca ccatctaaag gcccaggtgg acggccacat gctgacgccc 540 ctccggggca gggcagccct ctgggcctcc ttcactgctg tatccccatg cctaggactg 600 ctcctgcttt gtgataggtg ctcaataaac gcctgtggac cagaaaaaaa aaaaaaaaa 659 30 4 PRT Porcine Gen. Sp. 30 Tyr Arg Ser Leu 1 31 22 DNA Artificial sequence This sequence is the forward primer for RT-PCR amplification of PRRSV RNA 31 ccccattttc ctctagcgac tg 22 32 22 DNA Artificial sequence This sequence is a reverse primer for RT-PCR amplification of PRRSV RNA 32 cggccgcatg gttctcgcca at 22 33 20 DNA Artificial sequence This sequence is a forward primer for RT-PCR 33 cctacctggc cacagcctac 20 34 20 DNA Artificial sequence This sequence is a reverse primer for RT-PCR 34 acaggcgcag caggttccga 20 35 20 DNA Artificial sequence This sequence is a forward primer for RT-PCR 35 tgggctggca ttcttgaggc 20 36 21 DNA Artificial sequence This sequence is a reverse primer for RT-PCR 36 ttcgggccgc atggttctcg c 21 37 4 PRT Artificial sequence This sequence is a motif which has known RNa binding activity 37 Tyr Xaa Xaa Leu 1 38 859 DNA Porcine Gen. Sp. 38 cgccgccact gccggcctcg gacgcgtgga cgagcctcct caggaattct gtccacctgt 60 ctcagagagg agcggtcccc agcagccagc cccaggatgg gcgaattcgg cgagaagggc 120 gcgccatgcg gccaccgttt gcctcaagta cctgcttttc accttcaact gctgcttctg 180 gctggctggc ctggccgtca tggcagtggg catctggacg ctggccctca agagcgacta 240 catcagcctc ctggcctcgg gcacctacct ggccacagcc tacatcctag tggtggcggg 300 cattgttgtc atggtgaccg gtgttctggg ctgctgtgcc accttcaagg agcggaggaa 360 cctgctgcgg ctgtacttca tcctgctgct gctcatcttt ctgctggaga tcatcgccgg 420 agtcctggcc tacgtctact accagcagct gagtgcagag ctcaaggcga acctgaagga 480 cactctgagc aagcgctacc gccagccggg ccacgagggt gtgaccagcg ccacggataa 540 gctgcagcag gagttccact gctgtggcag caacaactcc caggactggc gggacagtga 600 gtggatcctc tcgggtgagg caggcgaccg tgtggttcct gacagctgct gcaagacggt 660 ggtggcgggc tgcgggcggc gggaccacgc ctccaacatc tacaaagtgg agggcggctg 720 catcaccagg ctggagacct tcatccggga gcacctgagg atcatcgggg ctgtgggcat 780 cggcatcgcc tgtgtgcagg tgttcggcat gatcttcacg tgctgcctgt acaagagcct 840 gaagctggag cactactga 859 

We claim:
 1. A method of ascertaining the susceptibility to PRRS infection in an animal comprising the steps of: obtaining a sample of cellular material of known origin from said animal; performing a CD 151 assay on said sample; and using the results of said assay as a measure of the susceptibility of said animal.
 2. The method of claim 1, said cellular material being selected from the group consisting of semen, blood, germplasm, ova, and sperm cells.
 3. The method of claim 1, said assay step including the step of extracting the RNA from said sample.
 4. The method of claim 3, further comprising the step of performing reverse-transcriptase PCR on said extracted RNA.
 5. The method of claim 1, said assay step including the step of quantifying the amount of detected CD
 151. 6. The method of claim 5, further including the step of comparing said quantified amount of CD 151 with a known standard for said cellular material sample.
 7. The method of claim 6, said known standard representing the average susceptibility of said animal.
 8. The method of claim 6, said known standard being determined by averaging a large number of quantified CD 151 amounts from cellular material samples of the same origin as said sample.
 9. A method of comparing the PRRSV infection susceptibility of an animal to a known standard of PRRSV infection susceptibility, said known standard being correlated with a CD 151 level for cellular material of known origin, comprising the steps of: obtaining a sample of cellular material of known origin from said animal; analyzing said sample to determine the CD 151 level in said animal; and comparing said determined CD 151 level from said sample with the CD 151 level of said known standard.
 10. The method of claim 9, said known standard being from the same origin as said sample.
 11. The method of claim 9, said analyzing step including the step of extracting the RNA from said sample.
 12. The method of claim 11, further comprising the step of performing reverse-transcriptase PCR on said extracted RNA.
 13. The method of claim 9, said analyzing step including the step of quantifying the amount of determined CD
 151. 14. The method of claim 9, said sample comprising a cellular material sample selected from the group consisting of semen, ova, blood, germplasm, and sperm cells.
 15. A method for determining if an animal is resistant to PRRSV infection comprising the steps of: obtaining a sample of cellular material from said animal; performing an assay for the presence of CD 151 in said sample; and determining if said animal is resistant to PRRSV infection by the presence or absence of CD 151 in said sample.
 16. The method of claim 15, said sample being of a known origin.
 17. The method of claim 15, said sample being selected from the group consisting of semen, ova, blood, germplasm, and sperm cells.
 18. A method of classifying PRRSV infection resistance in an animal comprising the steps of: obtaining a sample of cellular material of known origin from said animal; performing an assay on said sample to find the level of CD 151 in said sample; comparing said CD 151 level of said sample with a known scale of CD 151, said known scale corresponding to a specific degree of PRRSV infection resistance; and classifying said animal's PRRSV infection resistance based on said comparison with said scale.
 19. The method of claim 18, said classification resulting in a percentile ranking of PRRSV infection resistance in said animal.
 20. The method of claim 18, said sample being selected from the group consisting of blood, semen, ova, germplasm, and sperm sells.
 21. The method of claim 18, said known scale being a scale for cellular material of the same origin as said sample.
 22. The method of claim 18 wherein said known scales differ depending on the origin of said sample.
 23. The method of claim 18, said assay step including the step of extracting the RNA from said sample.
 24. The method of claim 23, further comprising the step of performing reverse-transcriptase PCR on said extracted RNA.
 25. A method for detecting CD 151 in a sample of cellular material comprising the steps of: extracting the RNA from said sample; performing reverse-transcriptase PCR on said extracted RNA; and analyzing said reverse-transcriptase PCR results for the presence of CD
 151. 26. The method of claim 25, further comprising the step of quantifying the amount of CD
 151. 27. The method of claim 25, said sample being of a known origin.
 28. The method of claim 25, said sample being selected from the group consisting of semen, ova, blood, germplasm, and sperm cells.
 29. A method of preparing PRRSV vaccine stock comprising the steps of: providing a cell line; transforming said cell line with CD 151; infecting said cell line with PRRSV; and causing said cell line to produce PRRSV progeny for use in said vaccine stock.
 30. The method of claim 29, said cell line being of non-simian origin.
 31. The method of claim 29, said cell line being non-susceptible to PRRSV infection prior to said transformation with CD
 151. 32. The method of claim 29, said transforming step including stable transfection with a plasmid containing a CD 151 DNA sequence.
 33. The method of claim 32, said CD 151 sequence having at least about 91% sequence homology with SEQ ID No.
 1. 34. The method of claim 33, said CD 151 sequence having at least about 95% sequence homology with SEQ ID No.
 1. 35. The method of claim 34, said CD 151 sequence having at least about 98% sequence homology with SEQ ID No.
 1. 36. The method of claim 29, said CD 151 sequence being of non-simian origin.
 37. The method of claim 36, said CD 151 sequence being of porcine origin.
 38. The method of claim 32, said CD 151 sequence having at least 84% sequence homology with SEQ ID No.
 14. 39. The method of claim 38, said CD 151 sequence having at least 90% sequence homology with SEQ ID No.
 14. 40. The method of claim 39, said CD 151 sequence having at least 95% sequence homology with SEQ ID No.
 14. 41. The method of claim 40, said CD 151 sequence having at least 98% sequence homology with SEQ ID No.
 14. 42. The method of claim 29, said vaccine stock of said transformed cell line being of higher titer than was previously obtainable prior to transformation.
 43. The method of claim 42, said titer of said transformed line being at least about 100 fold higher than was possible prior to transformation.
 44. A transformed cell line containing DNA coding for CD 151, said cell line, prior to transformation, not containing DNA coding for CD
 151. 45. The transformed cell line of claim 44, said cell line being of non-simian origin.
 46. The transformed cell line of claim 44, said DNA coding for CD 151 being of non-simian origin.
 47. The transformed cell line of claim 46, said DNA coding for CD 151 being of porcine origin.
 48. An isolated DNA sequence having at least about 91% sequence homology with SEQ ID No.
 1. 49. The DNA sequence of claim 48, said sequence having at least about 95% sequence homology with SEQ ID No.
 1. 50. The DNA sequence of claim 49, said sequence having at least about 98% sequence homology with SEQ ID No.
 1. 51. A plasmid containing a DNA sequence having at least about 91% sequence homology with SEQ ID No.
 1. 52. The plasmid of claim 51, said plasmid containing a DNA sequence having at least about 95% sequence homology with SEQ ID No.
 1. 53. The plasmid of claim 52, said plasmid containing a DNA sequence having at least about 98% sequence homology with SEQ ID No.
 1. 54. A plasmid having the Genbank accession number AF
 275666. 55. A plasmid containing a DNA sequence having at least 84% sequence homology with SEQ ID No.
 14. 56. The plasmid of claim 55, said plasmid containing a DNA sequence having at least 90% sequence homology with SEQ ID No.
 14. 57. The plasmid of claim 56, said plasmid containing a DNA sequence having at least 95% sequence homology with SEQ ID No.
 14. 58. The plasmid of claim 57, said plasmid containing a DNA sequence having at least 98% sequence homology with SEQ ID No.
 14. 59. A vector containing a DNA sequence having at least about 91% sequence homology with SEQ ID No.
 1. 60. The vector of claim 59, said vector containing a DNA sequence having at least about 95% sequence homology with SEQ ID No.
 1. 61. The vector of claim 60, said vector containing a DNA sequence having at least about 98% sequence homology with SEQ ID No.
 1. 62. A vector containing a DNA sequence having at least 84% sequence homology with SEQ ID No.
 14. 63. The vector of claim 62, said vector containing a DNA sequence having at least 90% sequence homology with SEQ ID No.
 14. 64. The vector of claim 63, said vector containing a DNA sequence having at least 95% sequence homology with SEQ ID No.
 14. 65. The vector of claim 64, said vector containing a DNA sequence having at least 98% sequence homology with SEQ ID No.
 14. 66. A method of rendering a cell line susceptible to PRRSV infection comprising the step of transforming said cell line using a plasmid containing CD151 coding sequences.
 67. The method of claim 66, said cell line being non-susceptible to PRRSV infection prior to said transforming step.
 68. The method of claim 66, said cell line being of non-simian origin.
 69. The method of claim 68, said cell line being of porcine origin.
 70. The method of claim 66, said plasmid containing a sequence having at least about 91% sequence homology with SEQ ID No.
 1. 71. The method of claim 70, said plasmid containing a sequence having at least about 95% sequence homology with SEQ ID No.
 1. 72. The method of claim 71, said plasmid containing a sequence having at least about 98% sequence homology with SEQ ID No.
 1. 73. The method of claim 66, said plasmid containing a sequence having the Genbank Accession No. AF
 275666. 74. The method of claim 66, said plasmid containing a sequence having at least 84% sequence homology with SEQ ID No.
 14. 75. The method of claim 74, said plasmid containing a sequence having at least 90% sequence homology with SEQ ID No.
 14. 76. The method of claim 75, said plasmid containing a sequence having at least 95% sequence homology with SEQ ID No.
 14. 77. The method of claim 76, said plasmid containing a sequence having at least 98% sequence homology with SEQ ID No.
 14. 78. A method of selecting animals for breeding comprising the steps of: screening a sample of cellular material from said animals for the presence of CD 151 to obtain a CD 151 level; comparing said CD 151 level with a known standard related to CD 151 levels; and selecting animals for breeding which had a CD 151 level lower than said known standard.
 79. The method of claim 78, said sample being of known origin.
 80. The method of claim 78, said sample being of the same origin as said known standard.
 81. The method of claim 78, said CD 151 level being at least about 20% lower than said known standard.
 82. The method of claim 81, said CD 151 level being at least about 35% lower than said known standard.
 83. The method of claim 82, said CD 151 level being at least about 50% lower than said known standard.
 84. The method of claim 78, said sample being selected from the group consisting of blood, semen, ova, germplasm, and sperm cells.
 85. A method of modifying PRRSV production in cells which are susceptible to PRRSV infection comprising the step of transforming said cells with CD
 151. 86. The method of claim 85, said modifying resulting in an increased production of PRRSV in said cells.
 87. The method of claim 85, said modifying resulting in the production of more PRRSV per milliliter of vaccine virus stock.
 88. The method of claim 85, said CD 151 being of non-porcine origin.
 89. The method of claim 88, said CD 151 being of porcine origin.
 90. A method of blocking entry of PRRSV into cells comprising the step of blocking PRRSV viral RNA from interaction with CD
 151. 91. The method of claim 90, said blocking step including contacting said cells with an anti-viral compound.
 92. The method of claim 91, said anti-viral compound being selected from the group consisting of anti-RNA entry compounds.
 93. The method of claim 92, said anti-viral compounds occupying binding sites on CD
 151. 94. The method of claim 93, said anti-viral compounds having greater affinity for said binding sites than said PRRSV viral RNA.
 95. The method of claim 93, said anti-viral compounds having greater avidity for said binding sites than said PRRSV viral RNA.
 96. The method of claim 93, said anti-viral compounds being screened in a high throughput manner.
 97. A method of diagnosing PRRSV infection in a swine herd comprising the steps of: obtaining a sample of cellular material from an individual swine in said herd; providing a CD 151 transformed cell line; performing an in vitro diagnostic test using said sample and said transformed cell line; and using the results of said diagnostic test to diagnose PRRSV infection.
 98. The method of claim 97, said cellular material being selected from the group consisting of blood, semen, ova, germplasm, and sperm cells.
 99. The method of claim 97, said diagnostic test being selected from the group consisting of virus isolation assays and immunodiagnostic assays.
 100. The method of claim 99, said immunodiagnostic assays being selected from the group consisting of ELISA, indirect fluorescent antibody tests, and indirect immunoperoxidase tests.
 101. The method of claim 97, said transformed cell line permitting greater virus replication than said cell line prior to transformation.
 102. The method of claim 97, said cell line being of non-simian origin.
 103. The method of claim 97, said transformed cell line including a CD 151 sequence of non-simian origin.
 104. A method of integrating CD 151 coding sequences directly into a chromosome comprising the steps of: providing a vector having CD 151 coding sequence therein; contacting a chromosome with said vector; and causing said CD 151 coding sequences to integrate with the chromosome.
 105. The method of claim 104, said vector being a retro-viral vector.
 106. The method of claim 104, further comprising the step of causing the expression of said coding sequences.
 107. The method of claim 104, said CD 151 coding sequences being selected from the group consisting of simian CD 151 and porcine CD
 151. 108. The method of claim 104, said CD 151 coding sequences having at least about 91% homology with SEQ ID No.
 1. 109. The method of claim 108, said CD 151 coding sequences having at least about 95% homology with SEQ ID No.
 1. 110. The method of claim 104, said CD 151 coding sequences having at least 84% sequence homology with SEQ ID No.
 14. 111. The method of claim 110, said CD 151 coding sequences having at least 90% sequence homology with SEQ ID No.
 14. 112. The method of claim 111, said CD 151 coding sequences having at least 95% homology with SEQ ID No.
 14. 113. The method of claim 112, said CD 151 coding sequences having at least 98% sequence homology with SEQ ID No.
 14. 114. A modified genome expressing an altered level of CD 151 in comparison to said genome prior to modification, said modification comprising an alteration in the number of CD 151 coding sequences in said genome.
 115. An animal having the modified genome of claim
 114. 116. An isolated mRNA sequence, said mRNA sequence corresponding to a DNA sequence having at least 84% sequence homology with SEQ ID No.
 38. 117. The mRNA sequence of claim 116, said DNA sequence having at least 90% sequence homology with SEQ ID No.
 38. 118. The mRNA sequence of claim 117, said DNA sequence having at least 95% sequence homology with SEQ ID No.
 38. 119. The mRNA sequence of claim 118, said DNA sequence having at least 98% sequence homology with SEQ ID No.
 38. 120. An isolated DNA sequence coding for CD 151, said DNA sequence having at least 84% sequence homology with SEQ ID No.
 14. 121. The isolated DNA sequence of claim 120, said DNA sequence having at least 90% sequence homology with SEQ ID No.
 14. 122. The isolated DNA sequence of claim 121, said DNA sequence having at least 95% sequence homology with SEQ ID No.
 14. 123. The isolated DNA sequence of claim 122, said DNA sequence having at least 98% sequence homology with SEQ ID No.
 14. 124. An isolated DNA sequence coding for CD 151, said sequence being derived from porcine CD
 151. 125. The isolated DNA sequence of claim 124, said sequence comprising a sequence selected from the group consisting of SEQ ID Nos. 15-29.
 126. The isolated DNA sequence of claim 125, said sequence including both introns and exons coding for CD
 151. 127. The isolated DNA sequence of claim 126, at least one of said introns having at least 84% sequence homology with a sequence selected from the group consisting of SEQ ID Nos. 16, 18, 21, 23, 25, 27 and
 29. 128. The isolated DNA sequence of claim 126, at least one of said exons having at least 84% sequence homology with a sequence selected from the group consisting of SEQ ID Nos. 15, 17, 19, 20, 22, 24, 26, and
 28. 129. A vaccine for inducing effective immunity against PRRSV, said vaccine comprising viral progeny produced in a non-simian cell line transformed with non-simian CD
 151. 130. The vaccine of claim 129, said CD 151 being of porcine origin.
 131. The vaccine of claim 129, said CD 151 having at least 84% sequence homology with SEQ ID No. 14
 132. A method of determining the effect of single nucleotide polymorphisms on PRRSV susceptibility comprising the steps of: obtaining at least two CD 151 genomic sequences; comparing single nucleotide polymorphisms between said sequences; and correlating said single nucleotide polymorphisms with susceptibility to PRRSV.
 133. A method of modulating viral RNA entry into cells comprising the step of altering the amount of CD 151 of said cells.
 134. The method of claim 133, said RNA entry resulting from endocytosis.
 135. The method of claim 133, said viral RNA being PRRSV RNA.
 136. A method of comparing PRRSV susceptibility factors between individual swine, said method comprising the steps of: obtaining the genetic sequence of at least two swine; analyzing the amount of CD 151 encoding sequences; and comparing the amount of CD 151 encoding sequences.
 137. A method of determining CD 151 sequences of swine comprising the steps of: taking a biopsy from a swine, said biopsy being taken from an ear notch or tail snip; and performing PCR on said biopsy to determine CD 151 sequences.
 138. The method of claim 137, including the step of using said determined CD 151 sequences and correlating expression levels with susceptibility to PRRSV. 